Fixed a infinite loop, updated libQuic, disabled MTU discovery and C API tweaks

[mpretty-cyro]

This PR contains 3 changes:

Fixed an infinite loop when refreshing the snode cache
We weren't defaulting the in_progress_snode_cache_refresh_count to 0 which meant when Network::refresh_snode_cache was called the recursive logic below would be called and when in_progress_snode_cache_refresh_count evaluated to a negative value it would just recurse endlessly

if (in_progress_snode_cache_refresh_count < num_snodes_to_refresh_cache_from)
        loop->call_soon([this, request_id]() { refresh_snode_cache(request_id); });

By defaulting the value to 0 this should no longer occur

Updated libQuic and disabled MTU discovery
Updated to the latest version of libQuic which adds the option to disable MTU discovery, this has been added to the network instance for the time being (in the future it'd be good to try to fix this a different way)

C API Tweaks
Updated a number of the C functions to take const char* const* instead of const char**