staging: ozwpan: fix memcmp() test in oz_set_active_pd()

"addr" is a pointer so it's either 4 or 8 bytes, but actually we want
to compare 6 bytes (ETH_ALEN).

As network stack already provides helper function
is_zero_ether_addr() we use that instead of memcmp

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Rupesh Gujare <rgujare@ozmodevices.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>