net/sched: act_tunnel_key: add support for "don't fragment"

extend "act_tunnel_key" to allow specifying TUNNEL_DONT_FRAGMENT.

Suggested-by: Ilya Maximets <[e-mail]>
Reviewed-by: Pedro Tammela <[e-mail]>
Acked-by: Jamal Hadi Salim <[e-mail]>
Signed-off-by: Davide Caratti <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/uapi/linux/tc_act/tc_tunnel_key.h

···
 					 */
 	TCA_TUNNEL_KEY_ENC_TOS,		/* u8 */
 	TCA_TUNNEL_KEY_ENC_TTL,		/* u8 */
+	TCA_TUNNEL_KEY_NO_FRAG,		/* flag */
 	__TCA_TUNNEL_KEY_MAX,
 };
 

net/sched/act_tunnel_key.c

···
 		    nla_get_u8(tb[TCA_TUNNEL_KEY_NO_CSUM]))
 			flags &= ~TUNNEL_CSUM;
 
+		if (nla_get_flag(tb[TCA_TUNNEL_KEY_NO_FRAG]))
+			flags |= TUNNEL_DONT_FRAGMENT;
+
 		if (tb[TCA_TUNNEL_KEY_ENC_DST_PORT])
 			dst_port = nla_get_be16(tb[TCA_TUNNEL_KEY_ENC_DST_PORT]);
 
···
 				   key->tp_dst)) ||
 		    nla_put_u8(skb, TCA_TUNNEL_KEY_NO_CSUM,
 			       !(key->tun_flags & TUNNEL_CSUM)) ||
+		    ((key->tun_flags & TUNNEL_DONT_FRAGMENT) &&
+		     nla_put_flag(skb, TCA_TUNNEL_KEY_NO_FRAG)) ||
 		    tunnel_key_opts_dump(skb, info))
 			goto nla_put_failure;