wifi: mwifiex: Set WIPHY_FLAG_NETNS_OK flag

Allow moving the wiphy device for mwififex to a non-inital network
namespace. Many wireless drivers enable this flag implicitly by
initializing through the generic ieee80211_alloc_hw_nm function. As
mwifiex does not utilize this function WIPHY_FLAG_NETNS_OK must be set
explicitly.

Moving to network namespace and working connection tested using
wpa_supplicant from a network namespace as well as from a container on
GyroidOS. The hardware was the Toradex Apalis i.MX8QM Board using the
Azurewave AW-CM276NF wireless module.

Signed-off-by: Johannes Wiesboeck <johannes.wiesboeck@aisec.fraunhofer.de>
Reviewed-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230706093437.3380526-1-johannes.wiesboeck@aisec.fraunhofer.de