MAJOR: sample: don't pass l7 anymore to sample fetch functions

All of them can now retrieve the HTTP transaction *if it exists* from
the stream and be sure to get NULL there when called with an embryonic
session.

The patch is a bit large because many locations were touched (all fetch
functions had to have their prototype adjusted). The opportunity was
taken to also uniformize the call names (the stream is now always "strm"
instead of "l4") and to fix indent where it was broken. This way when
we later introduce the session here there will be less confusion.
diff --git a/src/listener.c b/src/listener.c
index af8a524..5d459b6 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -590,21 +590,21 @@
 
 /* set temp integer to the number of connexions to the same listening socket */
 static int
-smp_fetch_dconn(struct proxy *px, struct stream *l4, void *l7, unsigned int opt,
+smp_fetch_dconn(struct proxy *px, struct stream *strm, unsigned int opt,
                 const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
 	smp->type = SMP_T_UINT;
-	smp->data.uint = strm_sess(l4)->listener->nbconn;
+	smp->data.uint = strm_sess(strm)->listener->nbconn;
 	return 1;
 }
 
 /* set temp integer to the id of the socket (listener) */
 static int
-smp_fetch_so_id(struct proxy *px, struct stream *l4, void *l7, unsigned int opt,
+smp_fetch_so_id(struct proxy *px, struct stream *strm, unsigned int opt,
                 const struct arg *args, struct sample *smp, const char *kw, void *private)
 {
 	smp->type = SMP_T_UINT;
-	smp->data.uint = strm_sess(l4)->listener->luid;
+	smp->data.uint = strm_sess(strm)->listener->luid;
 	return 1;
 }