Fix race condition that breaks BGP connections after reconfigure.

Fix race condition that breaks BGP connections after reconfigure.

RFC says that only connections in OpenConfirm and Established state
should participate in connection collision detection.

The current implementation leads to race condition when both sides
are trying to connect at the almost same time, then both sides
receive OPEN message by different connections at the almost same
time and close the other connection. Both connections are
closed and the both sides end in  start/idle or start/active
state.