This patch makes the necessary changes to make IPv6 dst_entry garbage
collection work with multiple network namespaces.

In ip6_dst_gc(), static local variables are now declared
per-namespace.
Signed-off-by: NBenjamin Thery <benjamin.thery@bull.net>
Signed-off-by: NDaniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>