Put jail(2) under COMPAT_FREEBSD11. It has been the "old" way of creating

Put jail(2) under COMPAT_FREEBSD11.  It has been the "old" way of creating
jails since FreeBSD 7.

Along with the system call, put the various security.jail.allow_foo and
security.jail.foo_allowed sysctls partly under COMPAT_FREEBSD11 (or
BURN_BRIDGES).  These sysctls had two disparate uses: on the system side,
they were global permissions for jails created via jail(2) which lacked
fine-grained permission controls; inside a jail, they're read-only
descriptions of what the current jail is allowed to do.  The first use
is obsolete along with jail(2), but keep them for the second-read-only use.

Differential Revision:	D14791