ssa.c: Join core node to itself rather than to "MASTER" core

Without the patch, after moving mastership to a new core, it's
distribution tree is wrong. There is no core there.

Also, distribution tree formation doesn't really support two cores
with one is standby.

Signed-off-by: Sasha Kotchubievsky <sashakot@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ssa.c: Handle opened upstream connection if a new parent is received

- If the old and new parents are identical and the connection is alive,
  just move to the CONNECTED state.
- If the parents are different, close the existing upstream connection.

Signed-off-by: Sasha Kotchubievsky <sashakot@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>