bge(4) and softint-based if_input

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

I am seeing very slow responses to received packets to a bge(4)
controller since the change to run if_input in a softint.

Sending works fine and other controllers on other machines are fine.

It seems worst under high load, copying a large file to the machine
with the bge(4) using NFS or FTP will trigger it, interactive sessions
still seem ok.

The bge(4) can process multiple packets in one call to the interrupt
handler, the interrupt mitigation feature is turned off though.

One thought was whether it would help to take out the call to
softint_schedule() from if_percpuq_enqueue() and call it explictly
after a batch of mbufs have been enqueued.

Robert Swindells