MINOR: resolvers: rework prototype suffixes to split resolving and dns.

A lot of prototypes in dns.h are specific to resolvers and must
be renamed to split resolving and DNS layers.
diff --git a/src/stream.c b/src/stream.c
index caac513..ff838b8 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -673,7 +673,7 @@
 		HA_SPIN_LOCK(DNS_LOCK, &resolvers->lock);
 		free(s->resolv_ctx.hostname_dn); s->resolv_ctx.hostname_dn = NULL;
 		s->resolv_ctx.hostname_dn_len = 0;
-		dns_unlink_resolution(s->resolv_ctx.requester);
+		resolv_unlink_resolution(s->resolv_ctx.requester);
 		HA_SPIN_UNLOCK(DNS_LOCK, &resolvers->lock);
 
 		pool_free(resolv_requester_pool, s->resolv_ctx.requester);