function retrieves the set of file descriptors which the calling
application should select on for reading and writing for the
processing of name service queries pending on the name service channel
File descriptors will be set in the file descriptor sets pointed to by
as appropriate. File descriptors already set in
will remain set; initialization of the file descriptor sets
is the responsibility of the caller.
returns one greater than the number of the highest socket set in either
If no queries are active,
will return 0.