common for both host and docker namespace (in multi-npu).

This change is triggered with issue found in multi-npu platforms
where in docker namespace
net.ipv6.conf.all.forwarding was 0 (should be 1) because of
which RS/RA message were triggered and link-local router were learnt.

Beside this there were some other sysctl.net.ipv6* params whose value
in docker namespace is not same as host namespace.

So to make we are always in sync in host and docker namespace
created common file that list all sysctl.net.* params and used
both by host and docker namespace. Any change will get applied
to both namespace.

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

only one and do string concatenation of all set commands