bonding: only set speed/duplex to unknown, if getting speed failed

bonding: only set speed/duplex to unknown, if getting speed failed

bond_update_speed_duplex() first set speed/duplex to unknown and
then asks slave driver for current speed/duplex. Since getting
speed/duplex might take longer there is a race, where this false state
is visible by /proc/net/bonding. With commit 691b2bf14946 ("bonding:
 update port speed when getting bond speed") this race gets more visible,
if user space is calling ethtool on a regular base.

Fix this by only setting speed/duplex to unknown, if link speed is
really unknown/unusable.

Fixes: 98f41f694f46 ("bonding:update speed/duplex for NETDEV_CHANGE")
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Acked-by: Jay Vosburgh <jv@jvosburgh.net>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260203141153.51581-1-tbogendoerfer@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>