carl9170: remove fast channel change feature

carl9170: remove fast channel change feature

Marco Fonseca reported a issue with his carl9170 device:
"I'm seeing a problem with the carl driver. If I change channels
repeatedly on the 2.4ghz band, monitoring (e.g. tcpdump) will
eventually halt.  I've seen this on various versions of the carl
driver/firmware (both from 1.9.4 to 1.9.7)"
<http://marc.info/?l=linux-wireless&m=136381302428113>

The culprit was identified as "fast channel change feature" which
according to Adrian Chadd is: "... notoriously unreliable and
really only fully debugged on some very later chips."
<http://marc.info/?l=linux-wireless&m=136416984531380>

Therefore, this patch removes the fast channel change feature.
The phy will now always have to go through a cold reset when
changing channels, but it should no longer become deaf.

Cc: Marco Fonseca <marco@tampabay.rr.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>