bgpd: Don't stop hold timer in OpenConfirm State

bgpd: Don't stop hold timer in OpenConfirm State

Issue:

1. Initially BGP start listening to socket.
2. Start timer expires and BGP tries to connect to peer and moved
   to Idle->connect (lets say peer datastructre X)
3. Peer datastrcture Y FD-X receives OPEN and moved from Opensent->
   Openconfirm state and start the hold timer.
4. In the OpenConfirm state, the hold timer is stopped. So peer X
   waits for Keepalive message from peer. If the Keepalive message
   is not received, then it will be in OpenConfirm state for
   indefinite time.
5. Due to this it neither close the existing connection nor it will
   accept any connection from peer.

Fix:
In the OpenConfirm state, don't stop the hold timer.
 1. Upon receipt of a neighbor’s Keepalive, the state is moved to
    Established.
 2. But If the hold timer expires, a stop event occurs, the state
    is moved to Idle.
This is as per RFC.

Signed-off-by: Sarita Patra <saritap@vmware.com>