QUIC: added support for segmentation offloading. To improve output performance, UDP segmentation offloading is used if available. If there is a significant amount of data in an output queue and path is verified, QUIC packets are not sent one-by-one, but instead are collected in a buffer, which is then passed to kernel in a single sendmsg call, using UDP GSO. Such method greatly decreases number of system calls and thus system load.

--- a/src/os/unix/ngx_linux_config.h
+++ b/src/os/unix/ngx_linux_config.h
@@ -103,6 +103,10 @@ typedef struct iocb  ngx_aiocb_t;
 #include <linux/capability.h>
 #endif
 
+#if (NGX_HAVE_UDP_SEGMENT)
+#include <netinet/udp.h>
+#endif
+
 
 #define NGX_LISTEN_BACKLOG        511