mac80211: fix the increment of mesh precedence value

The mesh precedence value in ieee80211_channel_switch
should be incremented or set to 1 only if this is the
initiator of mesh channel switch. For non-initiator,
the precedence value has updated using the Mesh
Channel Switch Parameters element. Fix this.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>