[PATCH] iwlwifi: set fixed rate through debugfs

This patch adds fixed rate setting through debugfs

$ echo <rate_n_flags> > \
/sys/kernel/debug/ieee80211/phy<X>/stations/<mac>/rate_scale_table

Currently there is no way to turn to rate scaling working again.
Will be fixed in later.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>