Calling `UdpStocketState::set_gro` from `quinn`

[stormshield-fabs]

We are trying to update our dependency on quinn and would like to re-enable GRO on Windows, since we haven't encountered the problems described in https://github.com/quinn-rs/quinn/issues/2041 (yet..?).

https://github.com/quinn-rs/quinn/pull/2092 introduced the "off by default" behavior and a UdpSocketState::set_gro setter, but it looks like it cannot be easily called from quinn directly, because we never have access to this structure.

I've researched different options and would like to have some feedback about the best way to move forward:

1. we could add a set_gro method on the AsyncUdpSocket trait
2. if this is not acceptable for quinn (because it leaks a lower-level abstraction), the user could create a new runtime type and override Runtime::wrap_udp_socket to instantiate the UdpSocketState and call set_gro before returning the dyn AsyncUdpSocket.

@djc @mxinden @Ralith