[BugFix]hostcfgd,mgmt interface IP cannot be deleted IF gw wasn't given during config.

[ashutosh-cs]

Issue

When configuring a static IP on the management interface without a default gateway address, the static IP cannot be deleted.
This issue occurs due to how the data is handled in update_mgmt_iface().
This function is responsible for configuring and triggering a restart of interfaces-config.service.

This issue can occur during different scneraios like

• when eth0 is configured via openconfig-interfaces.yang model which doesn't even have an option of default gw in the yang model.
• If someone has an intention just to use static IPv6 without explicit gw as gw can be config by RA.
• If the a wrong config was done, and wants to remove the config.

config interface ip add <interface_name> <ip_addr> [default_gw]

config interface ip remove <interface_name> <ip_addr> [default_gw]

sudo config interface ip add eth0 3002::8/64

root@sonic:/home/admin# ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::5054:ff:fe12:3456  prefixlen 64  scopeid 0x20<link>
        inet6 3002::8  prefixlen 64  scopeid 0x0<global>
        ether 52:54:00:12:34:56  txqueuelen 1000  (Ethernet)
        RX packets 9  bytes 1722 (1.6 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 44  bytes 7205 (7.0 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


sudo config interface ip remove eth0 3002::8/64 

Fix

The fix updates the logic in update_mgmt_iface() to properly manage changes to a management interface’s configuration:

• If the configuration has changed, it updates the stored value and logs the update.
• If the new configuration is empty (not data), it removes the existing entry for that key and logs the removal.
• If there is no change, it does nothing.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: ashutosh-cs / name: Ashutosh (a7905aa, 665a2f5, 5318bb3, 113c9fc)

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