net: socionext: fix possible user-after-free in netsec_process_rx

Fix possible use-after-free in in netsec_process_rx that can occurs if
the first packet is sent to the normal networking stack and the
following one is dropped by the bpf program attached to the xdp hook.
Fix the issue defining the skb pointer in the 'budget' loop

Fixes: ba2b2321 ("net: netsec: add XDP support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>