Revert "net: xfrm: Localize sequence counter per network namespace"

This reverts commit 0cc68d05 as it
breaks the abi and we can't allow that at this point in time.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I21e6c33ac7011d8489e766fd9b5e32bd528dc456