ssa.c: Reopen downstream listening sockets

Upon IBV_EVENT_PORT_ACTIVE or returning to "MASTER" state
in core node, downstream listening socket(s) should be reopened.

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