syslogd: Pre-open null file descriptor

[jfree]

Summary

Open _PATH_DEVNULL before entering capability mode. Access to /dev/null
is needed for dup2() when piping commands.

[markj]

usr.sbin/syslogd/syslogd.c

882

I think you could reasonably abort the process if /dev/null isn't accessible. Then you don't need those nulldesc >= 0 checks.

3618–3619

There is a pre-existing buglet here in that pfd[0] and [1] are not closed if pdfork() fails.

[jfree]

Update after rebase and address Mark's comments

[jfree]

Remove some rebasing errors (consfile got declared twice)

[jfree]

The nulldesc descriptor is used in waitdaemon() so open it prior to calling waitdaemon()

[jfree]

Update after peerlist rebase, adding pidfile_remove()