events: add fields to mtu provider events

[toidiu]

On error it would be nice to also expose additional fields to help customers debug why the connection level mtu setting failed. Code

• connection_config: The connection level specific values (propagating the connection config after error makes this tricky to add)
• remote_addr: the remote address for which the connect mtu values were specified (the lifetime on SocketAddress<'a> makes this tricky to add)

enum DatagramDropReason {
    ...,
    InvalidMtuConfiguration {
        /// MTU configuration for the endpoint
        endpoint_mtu_config: MtuConfig,

        // TODO expose connection level mtu config.
        // connection_config: MtuConfig,
        
         // TODO expose the remote address.
        // remote_addr: SocketAddress<'a>,
    }
}