MINOR: buffer: convert most b_ptr() calls to c_ptr()

The latter uses the channel wherever a channel is known.
diff --git a/src/backend.c b/src/backend.c
index 70972b4..ea266f3 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -322,7 +322,7 @@
 	struct proxy    *px   = s->be;
 	unsigned int     plen = px->url_param_len;
 	unsigned long    len  = http_body_bytes(msg);
-	const char      *params = b_ptr(req->buf, -http_data_rewind(msg));
+	const char      *params = c_ptr(req, -http_data_rewind(msg));
 	const char      *p    = params;
 	const char      *start, *end;
 
@@ -412,7 +412,7 @@
 	ctx.idx = 0;
 
 	/* if the message is chunked, we skip the chunk size, but use the value as len */
-	http_find_header2(px->hh_name, plen, b_ptr(s->req.buf, -http_hdr_rewind(&txn->req)), &txn->hdr_idx, &ctx);
+	http_find_header2(px->hh_name, plen, c_ptr(&s->req, -http_hdr_rewind(&txn->req)), &txn->hdr_idx, &ctx);
 
 	/* if the header is not found or empty, let's fallback to round robin */
 	if (!ctx.idx || !ctx.vlen)
@@ -669,7 +669,7 @@
 				if (!s->txn || s->txn->req.msg_state < HTTP_MSG_BODY)
 					break;
 				srv = get_server_uh(s->be,
-						    b_ptr(s->req.buf, -http_uri_rewind(&s->txn->req)),
+						    c_ptr(&s->req, -http_uri_rewind(&s->txn->req)),
 						    s->txn->req.sl.rq.u_l);
 				break;
 
@@ -679,7 +679,7 @@
 					break;
 
 				srv = get_server_ph(s->be,
-						    b_ptr(s->req.buf, -http_uri_rewind(&s->txn->req)),
+						    c_ptr(&s->req, -http_uri_rewind(&s->txn->req)),
 						    s->txn->req.sl.rq.u_l);
 
 				if (!srv && s->txn->meth == HTTP_METH_POST)
diff --git a/src/channel.c b/src/channel.c
index ad309b8..b720024 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -98,7 +98,7 @@
 
 	memcpy(chn->buf->p, msg, len);
 	chn->buf->o += len;
-	chn->buf->p = b_ptr(chn->buf, len);
+	chn->buf->p = c_ptr(chn, len);
 	chn->total += len;
 	return -1;
 }
diff --git a/src/h1.c b/src/h1.c
index 8b8545d..f070116 100644
--- a/src/h1.c
+++ b/src/h1.c
@@ -14,6 +14,7 @@
 #include <common/config.h>
 #include <common/http-hdr.h>
 
+#include <proto/channel.h>
 #include <proto/h1.h>
 #include <proto/hdr_idx.h>
 
@@ -1291,7 +1292,7 @@
 	msg->sol = 0;
 	while (1) {
 		const char *p1 = NULL, *p2 = NULL;
-		const char *start = b_ptr(buf, msg->next + msg->sol);
+		const char *start = c_ptr(msg->chn, msg->next + msg->sol);
 		const char *stop  = b_tail(buf);
 		const char *ptr   = start;
 		int bytes = 0;
diff --git a/src/proto_http.c b/src/proto_http.c
index 7b7f46c..5d7fc98 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -1111,7 +1111,7 @@
 	c_rew(&s->req, rewind = http_hdr_rewind(&txn->req));
 
 	path = http_get_path(txn);
-	len = buffer_count(s->req.buf, path, b_ptr(s->req.buf, txn->req.sl.rq.u + txn->req.sl.rq.u_l));
+	len = buffer_count(s->req.buf, path, c_ptr(&s->req, txn->req.sl.rq.u + txn->req.sl.rq.u_l));
 
 	c_adv(&s->req, rewind);
 
@@ -1650,7 +1650,7 @@
 				req->flags |= CF_WAKE_WRITE;
 				return 0;
 			}
-			if (unlikely(ci_tail(req) < b_ptr(req->buf, msg->next) ||
+			if (unlikely(ci_tail(req) < c_ptr(req, msg->next) ||
 			             ci_tail(req) > req->buf->data + req->buf->size - global.tune.maxrewrite))
 				channel_slow_realign(req, trash.str);
 		}
@@ -5137,7 +5137,7 @@
 			return 0;
 		}
 
-		if (unlikely(ci_tail(rep) < b_ptr(rep->buf, msg->next) ||
+		if (unlikely(ci_tail(rep) < c_ptr(rep, msg->next) ||
 		             ci_tail(rep) > rep->buf->data + rep->buf->size - global.tune.maxrewrite))
 			channel_slow_realign(rep, trash.str);
 
@@ -9919,7 +9919,7 @@
 		msg = &smp->strm->txn->rsp;
 
 	len  = http_body_bytes(msg);
-	body = b_ptr(msg->chn->buf, -http_data_rewind(msg));
+	body = c_ptr(msg->chn, -http_data_rewind(msg));
 
 	block1 = len;
 	if (block1 > msg->chn->buf->data + msg->chn->buf->size - body)
@@ -11390,7 +11390,7 @@
 			msg = &smp->strm->txn->rsp;
 
 		len  = http_body_bytes(msg);
-		body = b_ptr(msg->chn->buf, -http_data_rewind(msg));
+		body = c_ptr(msg->chn, -http_data_rewind(msg));
 
 		block1 = len;
 		if (block1 > msg->chn->buf->data + msg->chn->buf->size - body)