wireless: Treat IPv6 diffserv the same as IPv4 for 802.11e

Wireless will select a different hardware queue based on the
top 3 bits of the diffserv field, for ipv4. Extend that queue
selection mechanism to ipv6, and make the calls orthogonal.

Signed-off-by: Dave Täht <dave.taht@bufferbloat.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>