tests: add a test for macvlan

Note that this test doesn't run in uns mode, even though we have support
for that. Without a full container engine, I couldn't think of a nice way
to pass a macvlan device into the zdtm "container" when in UNS mode.

v2: use the nsid_manip feature flag

travis-ci: success for series starting with [v10,01/11] net: pass the struct nlattrs to dump() functions
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>