MINOR: protocol: rename the ->bind field to ->listen

The function currently is doing both the bind() and the listen(), so
let's call it ->listen so that the bind() operation can move to another
place.
diff --git a/src/protocol.c b/src/protocol.c
index bf1b1c5..6ea6033 100644
--- a/src/protocol.c
+++ b/src/protocol.c
@@ -67,7 +67,7 @@
 	HA_SPIN_LOCK(PROTO_LOCK, &proto_lock);
 	list_for_each_entry(proto, &protocols, list) {
 		list_for_each_entry(listener, &proto->listeners, rx.proto_list) {
-			lerr = proto->bind(listener, msg, sizeof(msg));
+			lerr = proto->listen(listener, msg, sizeof(msg));
 
 			/* errors are reported if <verbose> is set or if they are fatal */
 			if (verbose || (lerr & (ERR_FATAL | ERR_ABORT))) {