netpoll: provide an IP ident in UDP frames

Let's fill IP header ident field with a meaningful value,
it might help some setups.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/netpoll.c

@@ -388,6 +388,7 @@ void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 	struct udphdr *udph;
 	struct iphdr *iph;
 	struct ethhdr *eth;
+	static atomic_t ip_ident;
 
 	udp_len = len + sizeof(*udph);
 	ip_len = udp_len + sizeof(*iph);
@@ -423,7 +424,7 @@ void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 	put_unaligned(0x45, (unsigned char *)iph);
 	iph->tos      = 0;
 	put_unaligned(htons(ip_len), &(iph->tot_len));
-	iph->id       = 0;
+	iph->id       = htons(atomic_inc_return(&ip_ident));
 	iph->frag_off = 0;
 	iph->ttl      = 64;
 	iph->protocol = IPPROTO_UDP;