IFF_ALLMULTI is set/unset to if_flags via if_mcast_op. To avoid data races on
if_flags, IFNET_LOCK was added for if_mcast_op. Unfortunately it produces
a deadlock so we want to remove added IFNET_LOCK by avoiding the data races by
another approach.
This fix introduces ec_flags to struct ethercom and stores IFF_ALLMULTI to it.
ec_flags is protected by ETHER_LOCK and thus IFNET_LOCK is no longer necessary
for if_mcast_op. Note that the fix is applied only to MP-safe drivers that
the data races matter.
In the kernel, IFF_ALLMULTI is set by a driver and used by the driver itself.
So changing the storing place doesn't break anything. One exception is
ioctl(SIOCGIFFLAGS); we have to include IFF_ALLMULTI in a result if needed to
export the flag as well as before.
A upcoming commit will remove IFNET_LOCK.
PR kern/54189
99ec0af5eb