net: Set dev->proto_down before changing carrier state

A subsequent patch will make netif_carrier_on() a NOP for net devices
that have protodown turned on so that they will not accidentally gain
carrier. As a preparation, set dev->proto_down before calling
netif_carrier_{off,on}().

Note that the only driver that supports protodown and has a notion of a
carrier is macvlan and it is calling netif_carrier_{off,on}() with RTNL
held.

No functional changes intended.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260507105906.891817-2-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>