Staging: w35und: remove macro magic from MLME_GetNextPacket()

This removes the macro magic from MLME_GetNextPacket() to de-obfuscate the
code.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>