Merge branch 'selftests-mirror-to-gretap-with-team'

Petr Machata says:

====================
A test for mirror-to-gretap with team in UL packet path

This patchset adds a test for "tc action mirred mirror" where the
mirrored-to device is a gretap, and underlay path contains a team
device.

In patch #1 require_command() is added, which should henceforth be used
to declare dependence on a certain tool.

In patch #2, two new functions, team_create() and team_destroy(), are
added to lib.sh.

The newly-added test uses arping, which isn't necessarily available.
Therefore patch #3 introduces $ARPING, and a preexisting test is fixed
to require_command $ARPING.

In patches #4 and #5, two new tests are added. In both cases, a team
device is on egress path of a mirrored packet in a mirror-to-gretap
scenario. In the first one, the team device is in loadbalance mode, in
the second one it's in lacp mode. (The difference in modes necessitates
a different testing strategy, hence two test cases instead of just
parameterizing one.)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>