Add support for ietf-ssh-server YANG

[troglobit]

The recently ratified IETF RFC model for SSH provides an server grouping that can be included in the Infix services model.

Scope:

• Enable disable service
• Change listening port
• ListenAddress¹
• Host key similar to NETCONF "genkey" setup

Future:

• Bind to a single interface
• Add support for certificates

Note: netopeer2-server use libssh for access on port 830. This should probably be handled by the NETCONF model and not the SSH server model.

Footnotes

1. which may also require sysctl setting net.ipv4.ip_nonlocal_bind=1, e.g., if binding to a dynamic address like 169.254.1.1, in very specific conditions -- one customer setup uses this for predictive addresses in a local setup with containers. ↩

[mattiaswal]

Blocked by #434, that includes the latest SSH model

[mattiaswal]

The netconf model just includes parts of the ssh model for SSH transport. @troglobit

[troglobit]

Looks like it might be better to just extend infix-services.yang.

Update Oct 1: extend infix-services.yang with a uses ... from ietf-ssh-server.yang, with some heavy redactions (deviations).