[IPV6] put appropriate checksum for rawv6 sockets even if it was not initialized.

net/ipv6/raw.c

@@ -481,6 +481,10 @@ static int rawv6_push_pending_frames(struct sock *sk, struct flowi *fl, struct r
 		}
 	}
 
+	/* in case cksum was not initialized */
+	if (unlikely(*csum))
+		tmp_csum = csum_sub(tmp_csum, *csum);
+
 	*csum = csum_ipv6_magic(&fl->fl6_src,
 				&fl->fl6_dst,
 				len, fl->proto, tmp_csum);