srvctl syntax to add Oracle Messaging Gateway to scan listener

 Standalone databases using Messaging Gateway (mgw) need a special line in their tnsnames.ora resolving to the EXTPROC for mgw.  That doesn't change for clutserware.

The listener.ora for a stand-alone database has this additional information specific to mgw:

LSNRA =

  (DESCRIPTION_LIST =

    (DESCRIPTION =

      (ADDRESS_LIST =

        (ADDRESS = (PROTOCOL = TCP)(HOST = xyz1234)(PORT = 9999))

        (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))

      )

    )

  )

SID_LIST_LSNRA =

  (SID_LIST =

    (SID_DESC =

      (SID_NAME = orcla)

      (ORACLE_HOME = /u01/product/11.2.0.3)

    )

    (SID_DESC =

      (SID_NAME = mgwextproc)

      (ORACLE_HOME=/u01/product/11.2.0.3)

      (PROGRAM = extproc)

      (ENVS="LD_LIBRARY_PATH=/u01/product/11.2.0.3/jdk/jre/lib/amd64:/u01/product/11.2.0.3/jdk/jre/lib/amd64/server:/u01/product/11.2.0.3/lib")