staging: brcm80211: remove usage of ETHER_MAX_LEN definition

The linux include file if_ether.h already provides a definition
ETH_FRAME_LEN although this is excluding checksum. So code uses
ETH_FRAME_LEN+ETH_FCS_LEN now.

Reviewed-by: Brett Rudley <brudley@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Dowan Kim <dowan@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>