tunnels: implement new --show-tunnels command

Add support for the new show-tunnels command. Support dump.

 # ethtool --show-tunnels \*
Tunnel information for eth0:
  UDP port table 0:
    Size: 4
    Types: vxlan
    No entries
  UDP port table 1:
    Size: 4
    Types: geneve, vxlan-gpe
    Entries (2):
        port 1230, vxlan-gpe
        port 6081, geneve

v2: htons -> ntohs

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
5 files changed