uwb: doc: add documentation for ASIE sysfs attribute

Document the /sys/class/uwb_rc/uwbN/ASIE sysfs attribute

Signed-off-by: Thomas Pugliese <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-class-uwb_rc

···
                 Reading returns the currently active channel, or -1 if
                 the radio controller is not beaconing.
 
+What:           /sys/class/uwb_rc/uwbN/ASIE
+Date:           August 2014
+KernelVersion:  3.18
+Contact:        [e-mail]
+Description:
+
+                The application-specific information element (ASIE)
+                included in this device's beacon, in space separated
+                hex octets.
+
+                Reading returns the current ASIE.  Writing replaces
+                the current ASIE with the one written.
+
 What:           /sys/class/uwb_rc/uwbN/scan
 Date:           July 2008
 KernelVersion:  2.6.27