selftests: forwarding: Delete IPv6 address at the end

selftests: forwarding: Delete IPv6 address at the end

When creating the second host in h2_create(), two addresses are assigned
to the interface, but only one is deleted. When running the test twice
in a row the following error is observed:

$ ./router_bridge_vlan.sh
TEST: ping                                                          [ OK ]
TEST: ping6                                                         [ OK ]
TEST: vlan                                                          [ OK ]
$ ./router_bridge_vlan.sh
RTNETLINK answers: File exists
TEST: ping                                                          [ OK ]
TEST: ping6                                                         [ OK ]
TEST: vlan                                                          [ OK ]

Fix this by deleting the address during cleanup.

Fixes: 5b1e7f9ebd56 ("selftests: forwarding: Test routed bridge interface")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>