s3: nmbd: Ensure NetBIOS names are only 15 characters stored.

s3: nmbd: Ensure NetBIOS names are only 15 characters stored.

This screws up if the name is greater than MAX_NETBIOSNAME_LEN-1 in the
unix charset, but less than or equal to MAX_NETBIOSNAME_LEN-1 in the DOS
charset, but this is so old we have to live with that.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=10920

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit 7467f6e72cba214eeca75c34e9d9fba354c7ef31)
Signed-off-by: Andreas Schneider <asn@samba.org>