[mdns] Add API to remove mdns host IPv6 addresses

[mdns] Fix handling of SRP client Update message

Signed-off-by: Marius Preda <marius.preda@nxp.com>

[border-router] add border router features to OpenThread

	This commit adds border router functionality to the
	OpenThread stack

[mesh-forwarder] only mark Key ID Mode 0 and 1 as secure

Thread Reference 2020-08-18.

Thread Reference 2019-11-13.

Thread Reference 2018-09-26.

Thread Reference 2018-06-19.

Thread Reference 2017-07-16.