nl80211: Clean up if_add() for hostapd use

nl80211: Clean up if_add() for hostapd use

The allocation of new_bss and its use was separated by a lot of code in
this function. This can be cleaned up by moving the allocation next to
the use, so that this all can be within a single #ifdef HOSTAPD block.
The i802_check_bridge() call was outside type == WPA_IF_AP_BSS case, but
in practice, it is only used for WPA_IF_AP_BSS (and if used for
something else, this would have resulted in NULL pointer dereference
anyway).

Signed-hostap: Jouni Malinen <j@w1.fi>