winbind: Set the parent->child sock nonblocking

The parent goes through wb_simple_trans_send(), which deals with short
writes fine.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

source3/winbindd/winbindd_dual.c

@@ -1688,6 +1688,7 @@ static bool fork_domain_child(struct winbindd_child *child)
 		}
 
 		child->sock = fdpair[1];
+		set_blocking(child->sock, false);
 		return True;
 	}