ssa.c: Handle opened upstream connection if a new parent is received

 - If the old and new parents are equal and connection is alive, just
   go to CONNECTED state.
 - If the parents are different, close existing upstream connection.
Revert "ssa.c: Refactor ssa_upstream_dev_even function."

This reverts commit e679a9224341eeaabab0686ea91555a85b30971e.