selftests: Fix IPv6 address bind tests

IPv6 allows binding a socket to a device then binding to an address
not on the device (__inet6_bind -> ipv6_chk_addr with strict flag
not set). Update the bind tests to reflect legacy behavior.

Fixes: 34d0302a ("selftests: Add ipv6 address bind tests to fcnal-test")
Reported-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>