bnxt: Detach page from page pool before sending up the stack

When running in XDP mode, pages come from the page pool, and should
be freed back to the same pool or specifically detached.  Currently,
when the driver re-initializes, the page pool destruction is delayed
forever since it thinks there are oustanding pages.

Fixes: 322b87ca ("bnxt_en: add page_pool support")
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>