Polling + fxp = input errors

[Andrew Pantyukhin]

FWIW, enabling polling on 6.1-RELEASE with fxp
interfaces resulted in input errors, visible through
"netstat -w1 -Ifxp0". Moreover, today I had to restart
the interface (down-up) after it hanged somehow.
We've got hz=500 on this box. Once I disabled
polling the errors disappeared altogether and
performance rose considerably.

fxp0 at pci0:7:0:  class=0x020000 card=0x10098086 chip=0x12298086 rev=0x08 hdr=0x00
    vendor   = 'Intel Corporation'
    device   = '82550/1/7/8/9 EtherExpress PRO/100(B) Ethernet Adapter'
    class    = network
    subclass = ethernet