net: change ndo_set_rx_mode_async return type to int

net: change ndo_set_rx_mode_async return type to int

Change the return type of ndo_set_rx_mode_async from void to int to
allow drivers to report failures back to the core stack. This is a
prerequisite for adding retry logic in the core when drivers fail to
program RX filters (e.g. bnxt VF when PF is unavailable).

All existing implementations return 0 for now, maintaining current
behavior.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260608154014.227538-2-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>