Remove deprecated jail global permission sysctls, and make jail(2) COMPAT_FREEBSD11

[jamie]

Summary

The old jail system had sysctls to set jail permissions for all jails (e.g. security.jail.mount_allowed), which were superseded by per-jail permissions (e.g. allow.mount). These old sysctls remain a constant source of confusion to users, who expect that setting the sysctl will change the behavior of existing jails. That the sysctl value at the time a jail is created may matter is a backward-compatibility hack that does little or nothing to relieve the confusion. So it's time for them to go.

Also, jail(2) has been replaced by jail_set(2) for a number of years now, and it really ought to retire - at least into the COMPAT world.

Test Plan

There are very few bits of core code that actually used either jail(2) or the old sysctls (they're apparent in the non-kernel parts of the diff). Make sure these still work as expected.

The trickier part is to assess the change to other code, notably jail-related ports such as ezjail. It might be the case that some of this software needs to be brought up to the current state of things.

[jamie]

As suggested by bz@, I've only removed the sysctls #ifdef BURN_BRIDGES.

[jamie]

Once again, this time actually updating the diff...

[jamie]

I'm keeping the sysctls around, though without COMPAT_FREEBSD11 (or with BURN_BRIDGES), they're read-only. This preserves the expected behavior for programs that want to find out what they're allowed to do before attempting it (e.g. rc.d/hostname and rc.d/zfs). But they will no longer be used to set global permissions for jails.

For a GENERIC kernel, i.e. COMPAT_FREEBSD11 and not BURN_BRIDGES, everything still works as before.