This patch fixes a panic that might occur, if the device is part of a mesh
and tries to send with a higher rate index than "0".

kernel BUG at net/mac80211/rate.c:239!
invalid opcode: 0000 [#1] SMP
[...]
 Call Trace:
 <IRQ> <0> ? invoke_tx_handlers+0x474/0xb57 [mac80211]
 ? __ieee80211_tx_prepare+0x260/0x2a8 [mac80211]
 ? ieee80211_master_start_xmit+0x300/0x43a [mac80211]
 ? __qdisc_run+0xde/0x1da
 ? net_tx_action+0xb4/0x102
 Kernel panic - not syncing: Fatal exception in interrupt
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>