Add higher security levels

With DDWRT we cant login with winscp anymore, error says "Couldn't agree a key exchange algorithim (available: diffle-hellman-group14-sha256,kexguess2@matt.ucc.asn.au)"

They had to revert to lesser security again to get winscp to connect.

What is diffle-hellman-group14-sha256? It looks like a typo. It should be diffie-hellman-group14-sha256 (which is supported by WinSCP).