mac80211: calculate skb hash early when using itxq

This avoids flow separation issues when using software encryption.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20200726130947.88145-2-nbd@nbd.name


Signed-off-by: Johannes Berg <johannes.berg@intel.com>