CVE-2022-50042: Missing Release of Memory after Effective Lifetime

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

net: genl: fix error path memory leak in policy dumping

If construction of the array of policies fails when recording non-first policy we need to unwind.

netlink_policy_dump_add_policy() itself also needs fixing as it currently gives up on error without recording the allocated pointer in the pstate pointer.