Make setproctitle(3) work in Capsicum capability mode. This makes
ctld(8) child processes to indicate initiator address and name in
their titles, similar to what iscsid(8) child processes do.

PR: 181352
Differential Revision: https://reviews.freebsd.org/D2363
Reviewed by: rwatson@, mjg@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation