When a channel switch announcement (CSA) happens either through an action frame or...

When a channel switch announcement (CSA) happens either through an action frame or a beacon, the sampling algorithm can get back responses with a rate of zero which result in rate index lookups that fail with -1 as a return value.

We just need to ignore these, as the sample rate control algorithm will recover quickly.

Previously, after a channel switch due to radar or command line channel change, we would see lots of error messages spewed to the logs about invalid rate indexes from the sample alg.  This just squelches those messages.

git-svn-id: http://madwifi-project.org/svn/madwifi/trunk@2799 0192ed92-7a03-0410-a25b-9323aeb14dbd