bnx2x: use the right build_skb() helper

build_skb() no longer accepts slab buffers. Since slab use is fairly
uncommon we prefer the drivers to call a separate slab_build_skb()
function appropriately.

bnx2x uses the old semantics where size of 0 meant buffer from slab.
It sets the fp->rx_frag_size to 0 for MTUs which don't fit in a page.
It needs to call slab_build_skb().

This fixes the WARN_ONCE() of incorrect API use seen with bnx2x.

Reported-by: Thomas Voegtle <tv@lio96.de>
Link: https://lore.kernel.org/all/b8f295e4-ba57-8bfb-7d9c-9d62a498a727@lio96.de/
Fixes: ce098da1

 ("skbuff: Introduce slab_build_skb()")
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230329000013.2734957-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>