Option to fully disable Telnet fallback for device connections

NetBrain currently falls back to Telnet for device connections when SSH fails, even when administrators have configured SSH as the preferred or forced protocol. This enhancement would introduce a setting that fully disables Telnet at the system level, preventing any fallback attempt regardless of SSH connection outcome. Organizations with security policies that prohibit Telnet use need assurance that no Telnet sessions can occur, and this control would let them enforce compliance without manual verification.