fix show dhcp_server ipv4 info when gateway is optional (sonic-net#24801)

gateway is optional field. In smartswitch use case, dhcp server runs in the switch and is used to offer addresses to DPU midplane. But we don't want to install default route over the midplane interface so gateway option is removed from DHCP server config. See sonic-net#24495 (comment).

Signed-off-by: Yue Gao <yuega2@cisco.com>
Signed-off-by: xiaweijiang <xiaweijiang@microsoft.com>

Author: yue-fred-gao

dockers/docker-dhcp-server/cli/show/plugins/show_dhcp_server.py

@@ -110,7 +110,7 @@ def info(db, dhcp_interface, with_customized_options):
     for key in dbconn.keys("CONFIG_DB", "DHCP_SERVER_IPV4|" + dhcp_interface):
         entry = dbconn.get_all("CONFIG_DB", key)
         interface = key.split("|")[1]
-        table.append([interface, entry["mode"], entry["gateway"], entry["netmask"], entry["lease_time"], entry["state"]])
+        table.append([interface, entry["mode"], entry.get("gateway", ""), entry["netmask"], entry["lease_time"], entry["state"]])
         if with_customized_options:
             table[-1].append(entry["customized_options@"] if "customized_options@" in entry else "")
     click.echo(tabulate(table, headers=headers, tablefmt="grid"))