net: wwan: iosm: fix recursive lock acquire in unregister

Calling unregister_netdevice() inside wwan del link is trying to
acquire the held lock in ndo_stop_cb(). Instead, queue net dev to
be unregistered later.

Signed-off-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>