brcmfmac: Create netdev before returning from add_virtual_intf.

brcmfmac: Create netdev before returning from add_virtual_intf.

Currently netdev gets created possibly after returning from
add_virtual_intf. This is because add_if is handled asynch. This
is wrong and netdev should be up before returning.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Piotr Haber <phaber@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>