smb: throw out discovery timeout

it was only ever a safety net and shouldn't practically be necessary.
with the dust around the new discovery system having settled we should
probably deal with potentially getting stuck on discovery instead of
aborting the discovery through the safety net and hiding the defect.

also, technically speaking discovery could take longer than N seconds
since both WSD and NMB are broadcast systems without local caching
daemon like avahi, so they can be affected by network latency much more
than DNSSD