hep_udp listener: Fix "use_children" regression

Commit 899f65c introduced a regression where "use_children" would be
ignored for the HEP UDP protocol, possibly leading to extra forked
workers after an OpenSIPS upgrade, failed restarts due to exceeded MySQL
max connections, etc.

(cherry picked from commit 2801fae)

net/trans.h

@@ -73,7 +73,10 @@ extern struct proto_info protos[];
  */
 
 #define is_udp_based_proto(_p) \
-	(protos[_p].net.flags&PROTO_NET_USE_UDP)
+	((_p==PROTO_HEP_UDP) || protos[_p].net.flags&PROTO_NET_USE_UDP)
+/* XXX: ^ the PROTO_NET_USE_UDP concept is currently broken, since the macro
+ * may be used well before trans_load() is invoked, thus the "extra" protocols
+ * from @protos are still uninitialized and the macro will fail to see them */
 
 #define proto_has_listeners(_p) \
 	(protos[_p].listeners != NULL)

socket_info.c

@@ -161,7 +161,7 @@ static struct socket_info* new_sock_info( struct socket_id *sid)
 		memcpy(si->tag.s, sid->tag, si->tag.len+1);
 	}
 
-	if ( si->proto!=PROTO_UDP && si->proto!=PROTO_SCTP ) {
+	if (!is_udp_based_proto(si->proto)) {
 		if (sid->workers)
 			LM_WARN("number of workers per non UDP-based <%.*s> listener not "
 				"supported -> ignoring...\n", si->name.len, si->name.s);