[NETFILTER]: don't use nested attributes for conntrack_expect

We used to use nested nfattr structures for ip_conntrack_expect.  This is
bogus, since ip_conntrack and ip_conntrack_expect are communicated in
different netlink message types.  both should be encoded at the top level
attributes, no extra nesting required.  This patch addresses the issue.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>