ssa.c: In downstream handler, optimize rsock search when DB update msg received from access

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ssa.c: Move comment in ssa_downstream_handler

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ssa.c: Minor code refactoring in ssa_downstream_handler

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