ipv4: fix checksum annotation in udp4_csum_init

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

commit b46d9f62 upstream.
Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
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/ipv4/udp.c

@@ -1755,8 +1755,11 @@ static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
 		}
 	}
 
-	return skb_checksum_init_zero_check(skb, proto, uh->check,
-					    inet_compute_pseudo);
+	/* Note, we are only interested in != 0 or == 0, thus the
+	 * force to int.
+	 */
+	return (__force int)skb_checksum_init_zero_check(skb, proto, uh->check,
+							 inet_compute_pseudo);
 }
 
 /*