net/fq_impl: use skb_get_hash instead of skb_get_hash_perturb

This avoids unnecessarily regenerating the skb flow hash

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20200726130947.88145-1-nbd@nbd.name


[small commit message fixup]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>