net/quinn: Improve datagram handling

• net/quinn: Improve datagram handling
  We now check if the peer actually supports Datagram and refusing to proceed if it does not. Since the datagram size can actually change over the lifetime of a connection according to variation in path MTU estimate, also check buffer size before trying to send.

• net/quinn: Allow setting some parameters from TransportConfig
  As of now, we expose the below four properties from TransportConfig.

  • Initial MTU
  • Minimum MTU
  • Datagram receive buffer size
  • Datagram send buffer size

  Maximum UDP payload size from EndpointConfig and upper bound from MtuDiscoveryConfig are also exposed as properties.

  See the below documentation for further details.

  • https://docs.rs/quinn/latest/quinn/struct.TransportConfig.html
  • https://docs.rs/quinn/latest/quinn/struct.MtuDiscoveryConfig.html
  • https://docs.rs/quinn/latest/quinn/struct.EndpointConfig.html

  While at it, also clean up passing function parameters to the functions in utils.rs.

• net/quinn: Update quinn to 0.11.2

• net/quinn: Add stats property for connection statistics

Fixes #561 (closed).