tc: Fix binding of gact action by index.

tc: Fix binding of gact action by index.

The following operation fails:
% sudo tc actions add action pipe index 1
% sudo tc filter add dev lo parent ffff: \
       protocol ip pref 10 u32 match ip src 127.0.0.2 \
       flowid 1:10 action gact index 1

Bad action type index
Usage: ... gact <ACTION> [RAND] [INDEX]
Where:  ACTION := reclassify | drop | continue | pass | pipe |
                  goto chain <CHAIN_INDEX> | jump <JUMP_COUNT>
        RAND := random <RANDTYPE> <ACTION> <VAL>
        RANDTYPE := netrand | determ
        VAL : = value not exceeding 10000
        JUMP_COUNT := Absolute jump from start of action list
        INDEX := index value used

However, passing a control action of gact rule during filter binding works:

% sudo tc filter add dev lo parent ffff: \
       protocol ip pref 10 u32 match ip src 127.0.0.2 \
       flowid 1:10 action gact pipe index 1

Binding by reference, i.e. by index, has to consistently work with
any tc action.

Since tc is sensitive to the order of keywords passed on the command line,
we can teach gact to skip parsing arguments as soon as it sees 'gact'
followed by 'index' keyword.

Signed-off-by: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>