fix vlan in 8139cp on big-endian

Layout of opts2 is
: MSB(vlan_tag) : LSB(vlan_tag) : flags : 0 :
regardless of the host endianness.  On little-endian
the current code ends up with the right values, but
on big-endian it blows.  In r8169.c the same bug
had been fixed in commit d35da12a40426184b1d0844104b1d464753eba19
(r8169: endianness fixes).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>