There are various cases where we modify the inp_vflag and inp_inc.inc_flags
fields during a syscall, but don't restore those fields if the operation
fails. This can leave the inp structure in an inconsistent state and cause
various problems.

Restore the inp_vflag and inp_inc.inc_flags fields when the underlying
operation fails and the inp could be in an inconsistent state.

This is a direct commit to the branch as the code is different enough in
the other branches to make it difficult to resolve a merge.

Submitted by: jtl@
Reported by: Jakub Jirasek, Secunia Research at Flexera
Reviewed by: jhb@
Approved by: so
Security: FreeBSD-EN-18:11.listen
Security: CVE-2018-6925