uapi: netfilter_arp: use __u8 instead of u_int8_t

Similarly, the u_int8_t type is non-standard and not defined.  Change
it to use __u8 like the rest of the netfilter headers.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter_arp/arpt_mangle.h

@@ -13,7 +13,7 @@ struct arpt_mangle
 	union {
 		struct in_addr tgt_ip;
 	} u_t;
-	u_int8_t flags;
+	__u8 flags;
 	int target;
 };