Use driver locking to make Avahi-compat safe
Use driver locking to make Avahi-compat safe

Driver level locking ensures only one thread will execute code in the
driver at a time.

Fixes issue #5.

benoitc/dnssd_erlang,amolenaar/nerves_dnssd,PSPDFKit-labs/dnssd_erlang,PSPDFKit-labs/dnssd_erlang,benoitc/dnssd_erlang