MEDIUM: listener: keep a single thread-mask and warn on "process" misuse

Now that nbproc and nbthread are exclusive, we can still provide more
detailed explanations about what we've found in the config when a bind
line appears on multiple threads and processes at the same time, then
ignore the setting.

This patch reduces the listener's thread mask to a single mask instead
of an array of masks per process. Now we have only one thread mask and
one process mask per bind-conf. This removes ~504 bytes of RAM per
bind-conf and will simplify handling of thread masks.

If a "bind" line only refers to process numbers not found by its parent
frontend or not covered by the global nbproc directive, or to a thread
not covered by the global nbthread directive, a warning is emitted saying
what will be used instead.
diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index e4b8f63..28b7750 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -1076,7 +1076,7 @@
 	listener->state = LI_LISTEN;
 
 	fd_insert(fd, listener, listener->proto->accept,
-	          thread_mask(listener->bind_conf->bind_thread[relative_pid-1]));
+	          thread_mask(listener->bind_conf->bind_thread));
 
  tcp_return:
 	if (msg && errlen) {