testsuite: add a test for tc pedit action

testsuite: add a test for tc pedit action

This is not a full test, since kernel functionality is not actually
tested. It only compares that the kernel returned values when listing
the action are what one expects them to be.

Since this test succeeded on both a little-endian and a big-endian
system, it shows that any endianness issues have been resolved in
tc/p_ip.c at least.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>