NTB: handle link up, D0 and D3 events correctly

Just like for Link-Down event, Link-Up and D3 events
are also mutually exclusive to Link-Down and D0 events
respectively. So we clear the bitmasks in peer_sta
depending on event type.

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>