wil6210: add sysfs file for enable/disable fst link loss

The new "fst_link_loss" sysfs can be used to enable/disable the fst
link loss behavior for specific connection.

Change-Id: I7afcf86a575ca3add581c8823a3d5567483abcb0
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>