CVE-2026-72347: netfilter: xt_connmark: reject invalid shift parameters

In the Linux kernel, the following vulnerability has been resolved:

netfilter: xtconnmark: reject invalid shift parameters

Revision 2 of the CONNMARK target accepts user-controlled shift parameters and applies them to 32-bit mark values in connmarktgshift().

A shiftbits value of 32 or more triggers an undefined-shift bug when the rule is evaluated. Invalid shiftdir values are also accepted and silently fall back to the left-shift path.

Reject invalid revision-2 shift parameters in connmarktgcheck() so malformed rules fail at installation time, before they can reach the packet path.