[ZTP] Use config db instead of ZTP configuration profile while dhcp d…

[peter-yu]

[ZTP] Use config db instead of ZTP configuration profile while dhcp discovery

By adding USE_DEFAULT_CONFIG="no" in /etc/default/ztp for Inband ZTP, it won't generate /tmp/ztp_config_db.json, but use current redis config db during dhcp discovery.

This solves the interface breakout config reset to default mode (or other config, ex: FEC mode) and operation down issue.

[peter-yu]

@rajendra-dendukuri Can you help to review this PR? Thanks.

[rajendra-dendukuri]

Can you please elaborate on how these changes are used. In principle, I am OK with the changes but would like to understand the motivation and the use case.

[peter-yu]

There is a case that the inband port speed of DUT is 400G. As for the peer device, which connected to DUT, is with port speed of 100G. It requires to config port breakout on DUT and the fec (Forward Error Correction) mode in order to let the link up (same port speed, same fec mode with peer device). ex: breakout 400G to 100G, and fec=rs.
During inband ZTP process, these port attributes on DUT will be reset to factory default value, thus the link is down.

The PR would like to use the port configuration in config_db.json while DHCP discoveryprocess, thus it promise the link configuration correctness and let the link up.

This is enabled by adding USE_DEFAULT_CONFIG="no" in /etc/default/ztp for Inband ZTP.

Thanks.