ASACORE-777: mDNS for TCL/Router discovery

Use NGNS (mDNS) to discover Routing Nodes.

Send mDNS queries according to the new router discovery schedule. Listen for
mDNS responses unicasted to the thin client.

Legacy NS (version 1) queries are sent (and responses listened for) only when
the minimum allowed router protocol version is set to allow connection to
a legacy router.

Change-Id: Ie14b8315843ca9e2ae5f85090fc11d166f136aab
Signed-off-by: Peter Krystad <pkrystad@qce.qualcomm.com>