Make both iSCSI initiator and target support base64 encoded CHAP data.

While all tested initiators and targets use hex-encoded CHAP data, RFC also
allows base64 encoding there, and Microsoft certificaition tool uses it.

Reviewed by:	trasz (earlier version)
MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274328 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f