iwl3945/iwlwifi: fix led bug when SW rfkill

Patch fixes the bug at
http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1903



when SW rfkill is invoked by 'iwconfig txpower off',
the existing connection disassociates and led off command is sent
to the device which returns error as rfkill is 'true'.

Patch fixes this by just avoiding sending the led off/on command when
disassociated. The main purpose of the led_disassociate callback
is to start or stop the blinking.
There are three states in led
1) Always on when radio is on
2) Always off when radio is off
3) blink when associated and if there is some traffic.

In this callback 'allow_blinking' needs to be set false
when associated, as LED will be always on.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>