In version 4.15 of iproute2 there was added support
for chain index in tc_filter [1].
Such version is available e.g. in Ubuntu 18.04 and it
has to be supported in l3_tc_lib regex to match
properly output of "tc filter" command.
[1] https://lwn.net/Articles/745643/
Closes-bug: #1809497
Change-Id: Id4066b5cff933ccd0dd3c751bf67b5d58af662d1
(cherry picked from commit e788d29458)