idpf: fix idpf_vport_splitq_napi_poll()

idpf: fix idpf_vport_splitq_napi_poll()

idpf_vport_splitq_napi_poll() can incorrectly return @budget
after napi_complete_done() has been called.

This violates NAPI rules, because after napi_complete_done(),
current thread lost napi ownership.

Move the test against POLL_MODE before the napi_complete_done().

Fixes: c2d548cad150 ("idpf: add TX splitq napi poll support")
Reported-by: Peter Newman <peternewman@google.com>
Closes: https://lore.kernel.org/netdev/20250520121908.1805732-1-edumazet@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Joshua Hay <joshua.a.hay@intel.com>
Cc: Alan Brady <alan.brady@intel.com>
Cc: Madhu Chittim <madhu.chittim@intel.com>
Cc: Phani Burra <phani.r.burra@intel.com>
Cc: Pavan Kumar Linga <pavan.kumar.linga@intel.com>
Link: https://patch.msgid.link/20250520124030.1983936-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>