ipv6: Fix error path to cancel the meseage

genlmsg_cancel() needs to be called in the error path of
inet6_fill_ifmcaddr and inet6_fill_ifacaddr to cancel
the message.

Fixes: 6ecf4c37 ("ipv6: enable IFA_TARGET_NETNSID for RTM_GETADDR")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20201112080950.1476302-1-zhangqilong3@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>