RDS: give up on half formed connections after 15s

RDS: give up on half formed connections after 15s

RDS relies on events to transition connections through a few
different states, but sometimes we get stuck and end up with
a half formed connection that is never able to finish

The other end has either wandered off or there are bugs in
other layers, and we end up with any future attempts from
the other end rejected because we're already working on a
connection attempt.

This patch changes things to give up on half formed connections
after 15 seconds.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Bang Nguyen <bang.nguyen@oracle.com>