wlcore: resume() only if sta is associated

mac80211's resume() callback might get called even if
the sta is not associated (but only up). The
resume sequence in this case results in configuring
the wake-up conditions of a non-started role, which
causes fw assertion.

Fix it by bailing out if the STA is not connected
(like we do on suspend()).

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <luca@coelho.fi>