__protocol_available usage?

[Andreas Jaeger]

glibc implements __protocol_available but apparently it's nowhere
used:-(

I get the following warning when compiling:
../sysdeps/unix/sysv/linux/if_index.c:250: warning: no previous prototype for `__protocol_available'

Where should we use __protocol_available?  Where should a prototype be
added?

Andreas
-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj