tc: fix parsing of the control action

tc: fix parsing of the control action

If the user didn't specify any control action, don't pop the command line
arguments: otherwise, parsing of the next argument (tipically the 'index'
keyword) results in an error, causing the following 'tc-testing' failures:

 Test a6d6: Add skbedit action with index
 Test 38f3: Delete skbedit action
 Test a568: Add action with ife type
 Test b983: Add action without ife type
 Test 7d50: Add skbmod action to set destination mac
 Test 9b29: Add skbmod action to set source mac
 Test e93a: Delete an skbmod action

Also, add missing parse for 'ok' control action to m_police, to fix the
following 'tc-testing' failure:

 Test 8dd5: Add police action with control ok

tested with:
 # ./tdc.py

test results:
 all tests ok using kernel 4.16-rc2, except 9aa8 "Get a single skbmod
 action from a list" (which is failing also before this commit)

Fixes: 3572e01a090a ("tc: util: Don't call NEXT_ARG_FWD() in __parse_action_control()")
Cc: Michal Privoznik <mprivozn@redhat.com>
Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>