MFC r256570:

Fix the witness warning that warned against calling uiomove() while holding
the 'vmmdev_mtx' in vmmdev_rw().

Rely on the 'si_threadcount' accounting to ensure that we never destroy the
VM device node while it has operations in progress (e.g. ioctl, mmap etc).

Approved by:	re (rodrigc)
MFC 256440, 256498:

 - Normalize jailname.  "example.com" is converted to "example_com".
 - Fix a bug that some $jail_{jname}_foo variables did not work.
 - Fix a bug which prevented $jail_devfs_ruleset from working[1].
 - Move $jail_parameters to the last of the configuraiton lines[1].
 - Fix "ifname|addr" syntax support in jail_{jname}_ip.
 - Create /var/run/jail_{jname}.id because ezjail-admin depends on it.

Reported by:	jase [1]
Approved by:	re (gjb)
Fix __free_pages() in the linux shim.

__free_pages() is actaully supposed to take a "struct page *" not
an address.

MFC: 256546

Approved by:	re