staging: brcm80211: removed packet macros for accessing sk_buff fields

With the packet storage type changed from void pointer to struct sk_buff
pointer there is no need for macros for accessing these fields through
casting. These can now be accessed directly.

Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>