iwlwifi: mvm: Move unused phy's to a default channel

When immediate quiet bit is set in CSA, the entire channel is blocked
by the firmware. It is expected that all the MACs will evacuate the
channel and the phy will be eventually either moved or removed.

Currently, the phy context is just unreferenced and thus, the quiet
bit is kept set and it will be impossible to TX on this phy, if we
will need to reuse it in the future.  This can be seen when doing a
channel switch with mode=1 (quiet) twice from channel X to Y and then
back to channel X.

Fix that, by moving the phy context to a default channel when not
referenced anymore.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>