Commit afb2e8b8913f131e5fb3a1031aacae3ab2b91287 ('tests: Store P2P
Device ifname in class WpaSupplicant') did not take into account the
possibility of capa.flags not existing in get_driver_status() and broke
WEXT test cases. Fix this by checking that capa.flags is present before
looking at its value.
Signed-off-by: Jouni Malinen <j@w1.fi>