Add initial backport support for network namespaces

Add initial backport support for network namespaces

We simply declare the overly used init_net sprinkled all over
the kernel, and declare its. All other code should that uses
network namespaces should be ifdef'd for now as well as
inclusion of net/net_namespace.h as we do not backport
the network namespace implemetnation at all, we simply
try to nullify its effect.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>