mwifiex: Do not change bss_type in change_virtual_intf

When user adds a virtual interface driver will set the
bss_type to the iface_type given by the user. When
supplicant is started on the same interface, a call to
change_virtual_intf will be triggered if if_type is not
NL80211_IFTYPE_STATION. Here driver should not update
it's bss_type, because bss_type is intended to indicate
the original iface_type and changing the same will defeat
the purpose of creating this interface.

Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>