MFC r272938:  Filter out duplicate AC_PATH_REGISTERED async events.
MFC r272938:  Filter out duplicate AC_PATH_REGISTERED async events.

Queued async events handling in CAM opened race, that may lead to duplicate
AC_PATH_REGISTERED events delivery during boot.  That was not happening
before r272935 because the driver was initialized later.  After that change
it started create duplicate ports in CTL.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase