tc: f_flower: add options support for erspan

tc: f_flower: add options support for erspan

This patch is to add TCA_FLOWER_KEY_ENC_OPTS_ERSPAN's parse and
print to implement erspan 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 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 erspan1 ingress
  # tc filter add dev erspan1 protocol ip parent ffff: \
      flower \
        enc_src_ip 10.0.99.192 \
        enc_dst_ip 10.0.99.193 \
        enc_key_id 11 \
        erspan_opts 1:2:0:0/1:255:0:0 \
        ip_proto udp \
        action mirred egress redirect dev eth1
  # tc -s filter show dev erspan1 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
       erspan_opts 1:2:0:0/1:255:0:0
       not_in_hw
         action order 1: mirred (Egress Redirect to device eth1) stolen
         index 1 ref 1 bind 1
         Action statistics:
         Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
         backlog 0b 0p requeues 0

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>