TUN-4597: Add a QUIC server skeleton

- Added a QUIC server to accept streams
- Unit test for this server also tests ALPN
- Temporary echo capability for HTTP ConnectionType

vendor/golang.org/x/sys/cpu/cpu_x86.s

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build (386 || amd64 || amd64p32) && gc
 // +build 386 amd64 amd64p32
 // +build gc
 
@@ -25,3 +26,27 @@ TEXT ·xgetbv(SB),NOSPLIT,$0-8
 	MOVL AX, eax+0(FP)
 	MOVL DX, edx+4(FP)
 	RET
+
+// func darwinSupportsAVX512() bool
+TEXT ·darwinSupportsAVX512(SB), NOSPLIT, $0-1
+    MOVB    $0, ret+0(FP) // default to false
+#ifdef GOOS_darwin   // return if not darwin
+#ifdef GOARCH_amd64  // return if not amd64
+// These values from:
+// https://github.com/apple/darwin-xnu/blob/xnu-4570.1.46/osfmk/i386/cpu_capabilities.h
+#define commpage64_base_address         0x00007fffffe00000
+#define commpage64_cpu_capabilities64   (commpage64_base_address+0x010)
+#define commpage64_version              (commpage64_base_address+0x01E)
+#define hasAVX512F                      0x0000004000000000
+    MOVQ    $commpage64_version, BX
+    CMPW    (BX), $13  // cpu_capabilities64 undefined in versions < 13
+    JL      no_avx512
+    MOVQ    $commpage64_cpu_capabilities64, BX
+    MOVQ    $hasAVX512F, CX
+    TESTQ   (BX), CX
+    JZ      no_avx512
+    MOVB    $1, ret+0(FP)
+no_avx512:
+#endif
+#endif
+    RET