Linux 6.18 compat: META (#18039)

Update the META file to reflect compatibility with the 6.18
kernel.

Signed-off-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>

Author: behlendorf

META

@@ -6,5 +6,5 @@ Release:       rc4
 Release-Tags:  relext
 License:       CDDL
 Author:        OpenZFS
-Linux-Maximum: 6.17
+Linux-Maximum: 6.18
 Linux-Minimum: 4.18