ctld: normalize iSCSI TargetName on login

Case-insensitive TargetName matching on logins was accidentally removed,
let's fix that by normalizing TargetName again according to RFC 3722.

PR: 294522
Fixes: 4b1aac931465f39c5c26bfa1d5539a428d340f20
Sponsored by: ConnectWise
MFC after: 1 week
Reviewed by: asomers, jhb
Approved by: asomers (mentor)
Differential Revision: https://reviews.freebsd.org/D56469