mac80211: reset connection idle when going offchannel

When we go offchannel mac80211 currently leaves alive the
connection idle monitor. This should be instead postponed
until we come back to our home channel, otherwise by the
time we get back to the home channel we could be triggering
unecesary probe requests. For APs that do not respond to
unicast probe requests (Nexus One is a simple example) this
means we essentially get disconnected after the probes
fails.

This patch has stable fixes for kernels [2.6.35+]

Cc: stable@kernel.org
Cc: Paul Stewart <pstew@google.com>
Cc: Amod Bodas <amod.bodas@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>