Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r235693:

Typo and mdoc(7) style fixes.

PR: 168117

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Fix typos, spelling, formatting and mdoc mistakes found by Nobuyuki while
translating these manual pages. Minor corrections by me.

Submitted by: Nobuyuki Koganemaru <n-kogane@syd.odn.ne.jp>

Fix a bunch of typos and spelling mistakes.

Cross-reference netstat(1) from netisr(9) since you can now use it to
monitor netisr status.

MFC after: 1 week
Sponsored by: Juniper Networks

Update epair(4) to the new netisr implementation and polish
things a bit:
- use dpcpu data to track the ifps with packets queued up,
- per-cpu locking and driver flags
- along with .nh_drainedcpu and NETISR_POLICY_CPU.
- Put the mbufs in flight reference count, preventing interfaces
from going away, under INVARIANTS as this is a general problem
of the stack and should be solved in if.c/netisr but still good
to verify the internal queuing logic.
- Permit changing the MTU to virtually everythinkg like we do for loopback.

Hook epair(4) up to the build.

Approved by: re (kib)

Add an optional callback function that will be invoked when a per-CPU
queue was drained. It will never fire for a directly dispatched packet.

You will most likely never want to use this for any ordinary netisr usage
and you will never blame netisr in case you try to use it and it does
not work as expected.

Reviewed by: rwatson

Remove a line break leaving a function return type attached to the old
function declaration bottom rather than the new function declaration
start.

Try again to add beginnings of netisr(8) man page: this time add
netisr.9.