netpoll: warn on netpoll_send_udp users who haven't disabled irqs

Make sure we catch future netpoll_send_udp users who use it without
disabling irqs and also as a hint for poll_controller users.
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/netpoll.c

@@ -380,6 +380,8 @@ void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 	static atomic_t ip_ident;
 	struct ipv6hdr *ip6h;
 
+	WARN_ON_ONCE(!irqs_disabled());
+
 	udp_len = len + sizeof(*udph);
 	if (np->ipv6)
 		ip_len = udp_len + sizeof(*ip6h);