staging: r8188eu: use is_multicast_ether_addr in os_dep/recv_linux.c

Use is_multicast_ether_addr instead of custom macro IS_MCAST, the
buffer is properly aligned.

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210823120106.9633-9-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>