[FS#1393] netifd: "ubus call network reload" can't remove the deprecated ipv6 prefix delegation on lan

[LEDE Bugs]

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FS#1393 - netifd: "ubus call network reload" can't remove the deprecated ipv6 prefix delegation on lan
User who did this - Kai Song (alfred.song)

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I found that after DHCPv6 wan connection is removed, the ipv6 prefix assignment has been removed from netifd database of lan interface.  It is just the ipv6 address assignment of br-lan is still there in linux protocol stack.
See dump below

1. Create a DHCPv4 and a DHCPv6 wan connection:

[CXNK001D8F15] /lib/netifd/proto # ifstatus lan 
{
	"up": true,
	"pending": false,
	"available": true,
	"autostart": true,
	"dynamic": false,
	"uptime": 1981,
	"l3_device": "br-lan",
	"proto": "static",
	"device": "br-lan",
	"updated": [
		"addresses"
	],
	"metric": 0,
	"dns_metric": 0,
	"delegation": true,
	"ipv4-address": [
		{
			"address": "192.168.1.1",
			"mask": 24
		}
	],
	"ipv6-address": [
		
	],
	"ipv6-prefix": [
		
	],
	"ipv6-prefix-assignment": [
		{
			"address": "2001:db8:ffff:f000::",
			"mask": 64,
			"preferred": 230,
			"valid": 455,
			"local-address": {
				"address": "2001:db8:ffff:f000::1",
				"mask": 64
			}
		}
	],
	"route": [
......
		
	}
}
[CXNK001D8F15] /lib/netifd/proto # 
[CXNK001D8F15] /lib/netifd/proto # ifconfig br-lan 
br-lan    Link encap:Ethernet  HWaddr 52:54:00:12:34:56  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2001:db8:ffff:f000::1/64 Scope:Global
          inet6 addr: fe80::5054:ff:fe12:3456/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1039 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7115 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:139429 (136.1 KiB)  TX bytes:3459249 (3.2 MiB)


2 Remove the DHCPv6 wan connection. As you can see in the dump below, the "ipv6-prefix-assignment" has been removed from netifd database, but ipv6 address assignment is still there.

[CXNK001D8F15] /lib/netifd/proto # ifstatus lan 
{
	"up": true,
	"pending": false,
	"available": true,
	"autostart": true,
	"dynamic": false,
	"uptime": 2100,
	"l3_device": "br-lan",
	"proto": "static",
	"device": "br-lan",
	"updated": [
		"addresses"
	],
	"metric": 0,
	"dns_metric": 0,
	"delegation": true,
	"ipv4-address": [
		{
			"address": "192.168.1.1",
			"mask": 24
		}
	],
	"ipv6-address": [
		
	],
	"ipv6-prefix": [
		
	],
	"ipv6-prefix-assignment": [
		
	],
	"route": [
		
	],
	"dns-server": [
		
	],
	"dns-search": [
		
	],
	"inactive": {
		"ipv4-address": [
			
		],
		"ipv6-address": [
			
		],
		"route": [
			
		],
		"dns-server": [
			
		],
		"dns-search": [
			
		]
	},
	"data": {
		
	}
}
[CXNK001D8F15] /lib/netifd/proto # ifconfig br-lan 
br-lan    Link encap:Ethernet  HWaddr 52:54:00:12:34:56  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: 2001:db8:ffff:f000::1/64 Scope:Global
          inet6 addr: fe80::5054:ff:fe12:3456/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1049 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7483 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:141206 (137.8 KiB)  TX bytes:3638760 (3.4 MiB)

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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1393#comment4391