acinclude: Enable builds up to Linux 5.8

Allow building openvswitch against Linux kernels up to and including
version 5.8.

Acked-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

acinclude.m4

@@ -167,10 +167,10 @@ AC_DEFUN([OVS_CHECK_LINUX], [
     AC_MSG_RESULT([$kversion])
 
     if test "$version" -ge 5; then
-       if test "$version" = 5 && test "$patchlevel" -le 5; then
+       if test "$version" = 5 && test "$patchlevel" -le 8; then
           : # Linux 5.x
        else
-          AC_ERROR([Linux kernel in $KBUILD is version $kversion, but version newer than 5.5.x is not supported (please refer to the FAQ for advice)])
+          AC_ERROR([Linux kernel in $KBUILD is version $kversion, but version newer than 5.8.x is not supported (please refer to the FAQ for advice)])
        fi
     elif test "$version" = 4; then
        : # Linux 4.x