tc: implement support for action terse dump

tc: implement support for action terse dump

Implement support for action terse dump using new TCA_ACT_FLAG_TERSE_DUMP
value of TCA_ROOT_FLAGS tlv. Set the flag when user requested it with
following example CLI (-br for 'brief'):

$ tc -s -br actions ls action tunnel_key
total acts 2

        action order 0: tunnel_key       index 1
        Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

        action order 1: tunnel_key       index 2
        Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

In terse mode dump only outputs essential data needed to identify the
action (kind, index) and stats, if requested by the user.

Signed-off-by: Vlad Buslov <vlad@buslov.dev>
Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David Ahern <dsahern@gmail.com>