tc: f_flower: add options support for vxlan

tc: f_flower: add options support for vxlan

This patch is to add TCA_FLOWER_KEY_ENC_OPTS_VXLAN's parse and
print to implement vxlan options support in m_tunnel_key, like
Commit 56155d4df86d ("tc: f_flower: add geneve option match
support to flower") for geneve options support.

Option is expressed a 32bit number for gbp only, and vxlan
doesn't support multiple options.

With this patch, users can add and dump vxlan options like:

  # ip link add name vxlan1 type vxlan dstport 0 external
  # tc qdisc add dev vxlan1 ingress
  # tc filter add dev vxlan1 protocol ip parent ffff: \
      flower \
        enc_src_ip 10.0.99.192 \
        enc_dst_ip 10.0.99.193 \
        enc_key_id 11 \
        vxlan_opts 65793/4008635966 \
        ip_proto udp \
        action mirred egress redirect dev eth1
  # tc -s filter show dev vxlan1 parent ffff:

     filter protocol ip pref 49152 flower chain 0 handle 0x1
       eth_type ipv4
       ip_proto udp
       enc_dst_ip 10.0.99.193
       enc_src_ip 10.0.99.192
       enc_key_id 11
       vxlan_opts 65793/4008635966
       not_in_hw
         action order 1: mirred (Egress Redirect to device eth1) stolen
         index 3 ref 1 bind 1
         Action statistics:
         Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
         backlog 0b 0p requeues 0

v1->v2:
  - get_u32 with base = 0 for gbp.
v2->v3:
  - implement proper JSON array for opts.
v3->v4:
  - keep the same format between input and output, json and non json.
  - print gbp as uint.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David Ahern <dsahern@gmail.com>