Make kernel print jail ID when logging a process exit.

[marieheleneka_gmail.com]

Summary

Previously, when a process was killed (ex: core dumped), the kernel would log a message like this:
pid 74906 (top), uid 0: exited on signal 11 (core dumped)

The message now looks like this:
pid 66526 (top), jid: 1, uid 0: exited on signal 11 (core dumped)

"jid" will be 0 for processes not running in a jail, which is in line with other parts of the system. (ex: "ps -J 0" to show unjailed processes)
"jid" will be -1 if the jid information is unavailable for some reason. (this should ordinarily not happen, but I've not dug enough in the code to guarantee it won't ever happen.)

Suggested commit message:
Kernel now includes jail ID when logging a process exit. jid is 0 for unjailed processes.

Submitted by: Marie Helene Kvello-Aune <[e-mail]>
Sponsored by: Modirum MDPay
relnotes: yes

Test Plan

Apply patch, build & install kernel.
Spin up a few jails
Check dmesg output after running "kill -11" on a few jailed and unjailed processes.

[marieheleneka_gmail.com]

Fix whitespace

[mjg]

See this review https://reviews.freebsd.org/D27

[marieheleneka_gmail.com]

Added jid to log message for sigexit as well.
Made formatting more consistent (removed a colon)

[marieheleneka_gmail.com]

In D18618#397024, @mjg wrote:

See this review https://reviews.freebsd.org/D27

That diff looks interesting, and it made me realize I had missed sigexit. That's fixed now.

I much prefer D27's way of formatting things, but it seems to me it's dead in the water.

[marieheleneka_gmail.com]

Made code a bit more readable by storing jid as a variable, instead of double ?: syntax.
Fixed trailing whitespace.