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/stick_table.c b/src/stick_table.c
index f0f7808..79ab4fa 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -680,13 +680,13 @@
  *   smp      1        0     not possible
  *   smp      1        1     Present, last known value (eg: request length)
  */
-struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, struct stream *l4, void *l7,
+struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, struct stream *strm,
                                         unsigned int opt, struct sample_expr *expr, struct sample *smp)
 {
 	if (smp)
 		memset(smp, 0, sizeof(*smp));
 
-	smp = sample_process(px, l4, l7, opt, expr, smp);
+	smp = sample_process(px, strm, opt, expr, smp);
 	if (!smp)
 		return NULL;