Add attribute for TA max duration after last TA received. So that local
time is synchromous to other communicating OCB STAs. If the duration
expires, OCB STA without UTC time source is not in sync to other STAs
and stop scheduling DSRC channel switch after max duration.
Signed-off-by: Zhaoyang Liu <zhaoyang@codeaurora.org>
Signed-off-by: Ferry Zhou <tianguiz@codeaurora.org>