selftests: net: add missing config for amt.sh

stable inclusion
from stable-v6.6.33
commit 9d601b81f1fcd874dea0eac9a140ca861d4cf769
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IAD6H2

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d601b81f1fcd874dea0eac9a140ca861d4cf769

--------------------------------

[ Upstream commit c499fe96d3f75a5cf50de6089dd8f1cddd1301a9 ]

Test needs IPv6 multicast. smcroute currently crashes when trying
to install a route in a kernel without IPv6 multicast.

Fixes: c08e8bae ("selftests: add amt interface selftest script")
Link: https://lore.kernel.org/r/20240509161919.3939966-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Wang Hai <wanghai38@huawei.com>