mac80211.sh: add HT support for mesh

Hi

This is a quick patch to enable HT for mesh mode
https://github.com/cozybit/open80211s/wiki/HOWTO#high-throughput
http://lists.open80211s.org/pipermail/devel/2012-March/002990.html

For my test setup the speed increased from 1-2 Mbytes/sec to 8-10 Mbytes/sec (iperf)

I'm resending the patch because I’ve forgotten to increase PKG_RELEASE

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@free.fr>