OPTIM/MINOR: move the hdr_idx pools out of the proxy struct

It makes no sense to have one pointer to the hdr_idx pool in each proxy
struct since these pools do not depend on the proxy. Let's have a common
pool instead as it is already the case for other types.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index ed64457..dac6bca 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -44,6 +44,7 @@
 #include <proto/checks.h>
 #include <proto/dumpstats.h>
 #include <proto/frontend.h>
+#include <proto/hdr_idx.h>
 #include <proto/lb_chash.h>
 #include <proto/lb_fwlc.h>
 #include <proto/lb_fwrr.h>
@@ -5991,10 +5992,6 @@
 							     curproxy->nb_rsp_cap * sizeof(char *),
 							     MEM_F_SHARED);
 
-		curproxy->hdr_idx_pool = create_pool("hdr_idx",
-						     MAX_HTTP_HDR * sizeof(struct hdr_idx_elem),
-						     MEM_F_SHARED);
-
 		/* first, we will invert the servers list order */
 		newsrv = NULL;
 		while (curproxy->srv) {
@@ -6598,6 +6595,10 @@
 		}
 	}
 
+	pool2_hdr_idx = create_pool("hdr_idx",
+				    MAX_HTTP_HDR * sizeof(struct hdr_idx_elem),
+				    MEM_F_SHARED);
+
 	if (cfgerr > 0)
 		err_code |= ERR_ALERT | ERR_FATAL;
  out: