ssa.c: In ssa_downstream_svc_server, add peer LID log message

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ssa.c: In ssa_upstream_initiate_conn, add destination LID to log message

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
plugin/core.c: Move duplicated code into a single method

Add ssa_extract_update_ready_process() method for
processing SSA_DB_UPDATE_READY messages in extract
handler to factor out duplicated code.

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