ipv6: fix checksum annotation in udp6_csum_init

BugLink: https://bugs.launchpad.net/bugs/1878232

commit c148d163 upstream.

Cc: Tom Herbert <tom@herbertland.com>
Fixes: 4068579e ("net: Implmement RFC 6936 (zero RX csums for UDP/IPv6")
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/ipv6/ip6_checksum.c

@@ -84,9 +84,12 @@ int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
 	 * we accept a checksum of zero here. When we find the socket
 	 * for the UDP packet we'll check if that socket allows zero checksum
 	 * for IPv6 (set by socket option).
+	 *
+	 * Note, we are only interested in != 0 or == 0, thus the
+	 * force to int.
 	 */
-	return skb_checksum_init_zero_check(skb, proto, uh->check,
-					   ip6_compute_pseudo);
+	return (__force int)skb_checksum_init_zero_check(skb, proto, uh->check,
+							 ip6_compute_pseudo);
 }
 EXPORT_SYMBOL(udp6_csum_init);