net: netsec: start using buffers if page_pool registration succeeded

The current driver starts using page_pool buffers before calling
xdp_rxq_info_reg_mem_model(). Start using the buffers after the
registration succeeded, so we won't have to call
page_pool_request_shutdown() in case of failure

Fixes: 5c67bf0e ("net: netsec: Use page_pool API")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>