staging: brcm80211: clean up struct brcmf_if in fullmac

Some elements in structure brcmf_if are unused at all or
redundant. This patch cleans it up.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>