gss_krb5: Add upcall info indicating supported kerberos enctypes

The text based upcall now indicates which Kerberos encryption types are
supported by the kernel rpcsecgss code.  This is used by gssd to
determine which encryption types it should attempt to negotiate
when creating a context with a server.

The server principal's database and keytab encryption types are
what limits what it should negotiate.  Therefore, its keytab
should be created with only the enctypes listed by this file.

Currently we support des-cbc-crc, des-cbc-md4 and des-cbc-md5

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>