feat: tlsmiddlebox experiment (#817)

See https://github.com/ooni/probe/issues/2124

internal/engine/experiment/tlsmiddlebox/syscall_otherwise.go

@@ -0,0 +1,15 @@
+//go:build !cgo
+
+package tlsmiddlebox
+
+//
+// Disabled CGO for SO_ERROR
+//
+
+// getErrFromSockOpt returns the errno of the SO_ERROR
+//
+// This is the CGO_ENABLED=0 implementation of this function, which
+// always returns errno=0 for SO_ERROR
+func getErrFromSockOpt(fd uintptr) int {
+	return 0
+}