kernel: netfilter: nf_conntrack_h323: fix OOB read in decode_choice()

A flaw was found in the Linux kernel's nfconntrackh323 helper. A remote attacker could exploit this by sending a specially crafted Q.931 SETUP message to port 1720 through a firewall with the nfconntrackh323 helper active. This memory corruption vulnerability leads to an out-of-bounds read, which...