Add the first actually useful lookup method to the mslookup library: multicast
DNS.
The server side is added in a subsequent commit, when the mslookup server is
implemented for the osmo-hlr program.
Use custom DNS encoding instead of libc-ares (which we use in OsmoSGSN
already), because libc-ares is only a DNS client implementation and we will
need both client and server.
Resubmit of f10463c5fc after being
reverted in 110a49f69f. This new version
skips the mslookup_client_mdns test if multicast is not supported in the
build environment. I have verified that it doesn't break the build
anymore in my own OBS namespace.
Related: OS#4237, OS#4361
Patch-by: osmith, nhofmeyr
Change-Id: I3c340627181b632dd6a0d577aa2ea2a7cd035c0c
Oliver Smith
3a9f267983