RDMA/nes: don't leak skb if carrier down

Alternatively one could free the skb, OTOH I don't think this test is
useful so just remove it.

Cc: <linux-rdma@vger.kernel.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Doug Ledford <dledford@redhat.com>