avahi: add hash file

Help counteract upstream website issues, fixes:
http://autobuild.buildroot.net/results/103/103e5a62d16ed22414cc407eff8a78d5e8d7503c/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Tested-by: André Hentschel <nerv@dawncrow.de>
Reviewed-by: André Hentschel <nerv@dawncrow.de>
Acked-by: André Hentschel <nerv@dawncrow.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>