socket-util: Fix recursion issue in sendmmsg

The wrap_sendmmsg has infinite recursion issue.
Fix it by undef sendmmsg.

Signed-off-by: Zhenyu Gao <sysugaozhenyu@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/socket-util.c

@@ -1043,6 +1043,9 @@ sendmmsg(int fd, struct mmsghdr *msgs, unsigned int n, unsigned int flags)
     return emulate_sendmmsg(fd, msgs, n, flags);
 }
 #else
+/* sendmmsg was redefined in lib/socket-util.c, should undef sendmmsg here
+ * to avoid recursion */
+#undef sendmmsg
 int
 wrap_sendmmsg(int fd, struct mmsghdr *msgs, unsigned int n, unsigned int flags)
 {