There are various cases where we modify the inp_vflag and inp_inc.inc_flags

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