brcm80211: fmac: use brcmf_del_if for all net devices

Use brcmf_del_if for primary and virtual net device interfaces. This
is part of the net device interface clean up for fullmac.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>