mwifiex: do not process mgmt rx on uninitialized interface

This patch fixes a crash which was happening because of RX of
management frames on uninitialzed interface. Now we drop management
frames for interfaces where cfg80211 has not registered any management
subtype reception or interface has no NL80211 iftype set.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>