Send a network management event for a changed path MTU value.
Both IPv4 and IPv6 have their own events as we cannot mix these
because how the network event numbering space is implemented.
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
This adds generic code that can be used by both IPv4 and IPv6
Path MTU Discovery mechanism. The actual PMTU support for each
protocol family is in subsequent commits.
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>