refactor to mautrix 0.17.x; update deps

vendor/golang.org/x/sys/unix/syscall_solaris.go

@@ -158,7 +158,7 @@ func GetsockoptString(fd, level, opt int) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	return string(buf[:vallen-1]), nil
+	return ByteSliceToString(buf[:vallen]), nil
 }
 
 const ImplementsGetwd = true