Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Start respecting WITHOUT_INET6.

Make regression/priv compile again after the multi-IP jail
changes. Note that we are still using the legacy jail(2)
rather than the jail_set(2)/jail(3) syscall.
Add an IPv4, and an IPv6 loopback address in case we compile
with INET6 enabled.

Make the priv_vfs_extattr_system compile on amd64 as well using the
proper length modifier to printf(3) for ssize_t.

Reviewed by: rwatson
Approved by: re (kib)

Remove empty setup and cleanup functions for the pfkey test.

Add regression tests for privileged and supposedly unprivileged
IP_IPSEC_POLICY,IPV6_IPSEC_POLICY setsockopt cases.

We may need to review the current 'good' results to make
sure they reflect what we really want.

Discussed with: rwatson
Reviewed by: rwatson

In sys/netipsec/keysock.c rev. 1.19 a missing priv check was added.
Before that non-su users were able to open pfkey sockets as well.

Add a regression test so we can detect such problems in an automated way
in the future.