Fix string overflow that could occur during redirection due to passing
the wrong length to strlcpy(3). It looks like it could overflow into
the next field, isc_user, which is properly long to accomodate for it;
I don't think it could cause any harm other than breaking the connection.

Reviewed by: mav
MFC after: 2 weeks
Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D26247