tc: m_tunnel_key: add options support for erpsan

tc: m_tunnel_key: add options support for erpsan

This patch is to add TCA_TUNNEL_KEY_ENC_OPTS_ERSPAN's parse and
print to implement erspan options support in m_tunnel_key, like
Commit 6217917a3826 ("tc: m_tunnel_key: Add tunnel option support
to act_tunnel_key") for geneve options support.

Option is expressed as version:index:dir:hwid, dir and hwid will
be parsed when version is 2, while index will be parsed when
version is 1. erspan doesn't support multiple options.

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

  # ip link add name erspan1 type erspan external
  # tc qdisc add dev eth0 ingress
  # tc filter add dev eth0 protocol ip parent ffff: \
      flower indev eth0 \
        ip_proto udp \
        action tunnel_key \
          set src_ip 10.0.99.192 \
          dst_ip 10.0.99.193 \
          dst_port 6081 \
          id 11 \
          erspan_opts 1:2:0:0 \
      action mirred egress redirect dev erspan1
  # tc -s filter show dev eth0 parent ffff:

     filter protocol ip pref 49151 flower chain 0 handle 0x1
       indev eth0
       eth_type ipv4
       ip_proto udp
       not_in_hw
         action order 1: tunnel_key  set
         src_ip 10.0.99.192
         dst_ip 10.0.99.193
         key_id 11
         dst_port 6081
         erspan_opts 1:2:0:0
         csum pipe
           index 2 ref 1 bind 1
         ...
v1->v2:
  - no change.
v2->v3:
  - no change.
v3->v4:
  - keep the same format between input and output, json and non json.
  - print version, index, dir and hwid as uint.

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