mesh: Retransmit the last Commit Message in the Committed state

mesh: Retransmit the last Commit Message in the Committed state

Previously, mesh state machine transmits updated Commit Message when
receiving a Confirm Message in Committed state. According to the
standard, it should (re)send the latest Commit Message previously sent.

IEEE Std 802.11-2012, 11.3.8.6.4 Protocol instance behavior - Committed
state:
"Upon receipt of a Con event, ... If Sync is not greater than
dot11RSNASAESync, the protocol instance shall increment Sync, transmit
the last Commit Message sent to the peer, and set the t0
(retransmission) timer."

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>