ath5k: Disable fast channel switching by default

ath5k: Disable fast channel switching by default

BugLink: http://bugs.launchpad.net/bugs/767192

Disable fast channel change by default on AR2413/AR5413 due to
some bug reports (it still works for me but it's better to be safe).
Add a module parameter "fastchanswitch" in case anyone wants to enable
it and play with it.

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
(backported from commit a99168eece601d2a79ecfcb968ce226f2f30cf98 upstream)

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Herton Krzesinski <herton.krzesinski@canonical.com>
Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>