Clear IPv4 offload rules when tethering stopped

The condition for deleting IPv4 forwarding rules.
1. When the tethering client has gone, deletes the client and its
   rules.
2. When the upstream has gone, deletes all rules.
3. When the upstream has changed, deletes all rules.

Test: atest TetheringCoverageTests and check IPv4 offload rules
via dumpsys tethering in the following test cases.

Bug: 190783768

Test cases:
a. Loss upstream interface while tethering
  1. Enable WIFI tethering
  2. Disable upstream interface
  3. Check the rules are removed.
b. Loss downstream interfaces while tethering
  1. Enable WIFI tethering
  2. Enable BT tethering
  3. Disable BT tethering
  4. Check the BT tether rules are removed.
  5. Disable WIFI tethering
  6. Check the WIFI tether rules are removed.
c. Switch upstream interface while tethering
  1. Enable WIFI tethering
  2. Enable BT tethering
  3. Switch upstream interface from cellular to wifi.
  4. Check all rules are removed.
d. Enable NAT failure (manual)

Log:
The rule deletion in each case.
- IpServer#stopIPv4: case b and case d.
- BpfCoordinator#updateUpstreamNetworkState: case a and case c.

Test case a
06-23 09:58:59.245  [...] Tethering: [BpfCoordinator]
    updateUpstreamNetworkState tetherOffloadRule4Clear wlan2

Test case b
06-07 22:17:51.886  [..] Tethering: [bt-pan] cleanupUpstream bt-pan
06-07 22:17:51.888  [..] Tethering: [bt-pan] stopIPv4 bt-pan
06-07 22:18:23.769  [..] Tethering: [wlan2] cleanupUpstream wlan2
06-07 22:18:23.772  [..] Tethering: [wlan2] stopIPv4 wlan2

Test case c
06-08 11:11:48.277  [..] Tethering: [BpfCoordinator]
    updateUpstreamNetworkState tetherOffloadRule4Clear bt-pan
06-08 11:11:48.396  [..] Tethering: [BpfCoordinator]
    updateUpstreamNetworkState tetherOffloadRule4Clear wlan2
06-08 11:11:48.579  [..] Tethering: [wlan2] cleanupUpstreamInterface
    wlan2
06-08 11:11:48.808  [..] Tethering: [bt-pan] cleanupUpstreamInterface
    bt-pan

Enabling NAT failure
06-08 13:04:18.117  [..] Tethering: [wlan2] Exception enabling NAT [..]
06-08 13:04:18.234  [..] Tethering: [wlan2] cleanupUpstream wlan2
06-08 13:04:18.246  [..] Tethering: [wlan2] stopIPv4 wlan2

Change-Id: Id505a3deb277bbe0f44403234d8ca8bbf01eec80

0 files changed, 0 insertions, 0 deletions