Make the declaration of CheckTimeouts a proper C prototype.
Make the declaration of CheckTimeouts a proper C prototype.

This avoids a warning when including utp.h in C (not C++).

robgjansen/libutp,wujf/libutp,anacrolix/go-libutp,bittorrent/libutp,robgjansen/libutp,wujf/libutp,anacrolix/go-libutp,anacrolix/go-libutp,bittorrent/libutp,robgjansen/libutp,bittorrent/libutp,anacrolix/go-libutp,wujf/libutp