net: wwan: iosm: fix memory leak in ipc_wwan_dellink

In the Linux kernel, the following vulnerability has been resolved:

net: wwan: iosm: fix memory leak in ipc_wwan_dellink

IOSM driver registers network device without setting the

needs_free_netdev flag, and does NOT call free_netdev() when

unregisters network device, which causes a memory leak.

This patch sets needs_free_netdev to true when registers

network device, which makes netdev subsystem call free_netdev()

automatically after unregister_netdevice().