Returns the name associated with a socket.
    The $QIO equivalent is the IO$_SENSEMODE function with the p3
    argument.
    Format
      #include  <types.h>
      #include  <socket.h>
      int getsockname  ( int s, struct sockaddr *name, int *namelen
                       ); (_DECC_V4_SOURCE)
      int getsockname  ( int s, struct sockaddr *name, size_t
                       *namelen ); (not_DECC_V4_SOURCE)