use high bits from the mbuf flowid to pick a port to transmit on.

use high bits from the mbuf flowid to pick a port to transmit on.

a port here is a physical interface used by an aggr.

this leaves the low bits for a physical interface to use to pick a
tx ring. without this, aggr used low bits for port selection, which
takes bits away from the ring selection, which can lead to uneven
distribution of packets over tx rings.

ive been running this in production for well over a year now.