iproute_lwtunnel: add options support for geneve metadata

iproute_lwtunnel: add options support for geneve metadata

This patch is to add LWTUNNEL_IP(6)_OPTS and LWTUNNEL_IP_OPTS_GENEVE's
parse and print to implement geneve options support in iproute_lwtunnel.

Options are expressed as class:type:data and multiple options may be
listed using a comma delimiter, class and type are numbers and data
is a hex string.

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

  # ip netns add a
  # ip netns add b
  # ip -n a link add eth0 type veth peer name eth0 netns b
  # ip -n a link set eth0 up; ip -n b link set eth0 up
  # ip -n a addr add 10.1.0.1/24 dev eth0
  # ip -n b addr add 10.1.0.2/24 dev eth0
  # ip -n b link add geneve1 type geneve id 1 remote 10.1.0.1 ttl 64
  # ip -n b addr add 1.1.1.1/24 dev geneve1
  # ip -n b link set geneve1 up
  # ip -n b route add 2.1.1.0/24 dev geneve1
  # ip -n a link add geneve1 type geneve external
  # ip -n a addr add 2.1.1.1/24 dev geneve1
  # ip -n a link set geneve1 up
  # ip -n a route add 1.1.1.0/24 encap ip id 1 geneve_opts \
    1:1:1212121234567890,1:1:1212121234567890,1:1:1212121234567890 \
    dst 10.1.0.2 dev geneve1
  # ip -n a route show
  # ip netns exec a ping 1.1.1.1 -c 1

   1.1.1.0/24  encap ip id 1 src 0.0.0.0 dst 10.1.0.2 ttl 0 tos 0
     geneve_opts 1:1:1212121234567890,1:1:1212121234567890 ...

   PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
   64 bytes from 1.1.1.1: icmp_seq=1 ttl=64 time=0.079 ms

v1->v2:
  - improve the changelog.
  - use PRINT_ANY to support dumping with json format.
v2->v3:
  - implement proper JSON array for opts instead of just bunch of strings.
v3->v4:
  - keep the same format between input and output, json and non json.
  - print class and type as uint and print data as hex string.

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