FreeBSD: Make sure to destroy tap device for bridge

[metalefty]

This PR applies the same fix as well as #1859 for the bridge destination tap interface.

Behaviour after this PR

1. No tap interfaces before starting vpnbridge.

root@freebsd:~/SoftEtherVPN/build # ifconfig -a -g tap
root@freebsd:~/SoftEtherVPN/build #

2. Bridge tap device is created after starting vpnbridge.

root@freebsd:~/SoftEtherVPN/build # ./vpnbridge start
root@freebsd:~/SoftEtherVPN/build # ./vpncmd /server localhost /cmd:bridgelist
BridgeList command - Get List of Local Bridge Connection
Number|Virtual Hub Name|Network Adapter or Tap Device Name|Status
------+----------------+----------------------------------+---------
1     |BRIDGE          |bridge                            |Operating                        
The command completed successfully.         

root@freebsd:~/SoftEtherVPN/build # ifconfig -a -g tap
tap_bridge: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        description: SoftEther Virtual Network Adapter
        options=80000<LINKSTATE>
        ether 5e:d5:70:50:52:7d
        hwaddr 58:9c:fc:10:34:2a
        groups: tap
        media: Ethernet autoselect
        status: active
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        Opened by PID 757

3. All tap devices created by SoftEther are properly cleaned up after shutting down vpnbridge.

root@freebsd:~/SoftEtherVPN/build # ./vpnbridge stop
root@freebsd:~/SoftEtherVPN/build # ifconfig -a -g tap
root@freebsd:~/SoftEtherVPN/build #

Behaviour before this PR (e6123d3)

Tap device for bridge destination is not properly destroyed, remains after shutting down vpnbridge.

root@freebsd:~/SoftEtherVPN/build # ./vpnbridge start
root@freebsd:~/SoftEtherVPN/build # ifconfig -a -g tap
tap_bridge: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=80000<LINKSTATE>
        ether 5e:d5:70:50:52:7d
        hwaddr 58:9c:fc:10:34:2a
        inet 0.0.0.0 netmask 0xff000000 broadcast 255.255.255.255
        groups: tap
        media: Ethernet autoselect
        status: active
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        Opened by PID 1187

root@freebsd:~/SoftEtherVPN/build # ./vpnbridge stop
root@freebsd:~/SoftEtherVPN/build # ifconfig -a -g tap
tap_bridge: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=80000<LINKSTATE>
        ether 5e:d5:70:50:52:7d
        hwaddr 58:9c:fc:10:34:2a
        groups: tap
        media: Ethernet autoselect
        status: no carrier
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>

[metalefty]

I've done what I'm going to do with this PR.