igb: xsk: solve negative overflow of nb_pkts in zerocopy mode

igb: xsk: solve negative overflow of nb_pkts in zerocopy mode

There is no break time in the while() loop, so every time at the end of
igb_xmit_zc(), negative overflow of nb_pkts will occur, which renders
the return value always false. But theoretically, the result should be
set after calling xsk_tx_peek_release_desc_batch(). We can take
i40e_xmit_zc() as a good example.

Returning false means we're not done with transmission and we need one
more poll, which is exactly what igb_xmit_zc() always did before this
patch. After this patch, the return value depends on the nb_pkts value.
Two cases might happen then:
1. if (nb_pkts < budget), it means we process all the possible data, so
   return true and no more necessary poll will be triggered because of
   this.
2. if (nb_pkts == budget), it means we might have more data, so return
   false to let another poll run again.

Fixes: f8e284a02afc ("igb: Add AF_XDP zero-copy Tx support")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Link: https://patch.msgid.link/20250723142327.85187-3-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>