libsepol: trigger new RTM_GETLINK behavior

Use one of the policy config bits to tell the kernel to start using
the nlmsg_readpriv on RTM_GETLINK messages instead of the previous
hehavior of using nlmsg_read.

Bug: 141455849
Test: CtsSelinuxTargetSdkCurrentTestCases
Change-Id: I581af58247afe021d906f60153d5971cfaf14ab6
2 files changed