icmp: icmp_msgs_per_sec and icmp_msgs_burst sysctls become per netns

Previous patch made ICMP rate limits per netns, it makes sense
to allow each netns to change the associated sysctl.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20240829144641.3880376-4-edumazet@google.com


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