wlcore: cancel Tx watchdog on suspend and rearm on first Tx after

Sometimes a tx_flush during suspend fails, but the FW manages to flush
out the packets during the time when the host is supsended. Cancel
the Tx-watchdog on suspend to not cause a spurious recovery on resume
for that case. Set a flag to reinit the watchdog on the first Tx after
resume, so we'll still recover if the FW is not empty and there's
indeed a problem.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>