MFC r215017,215025:

MFC r215017,215025:
  Follow the lead of vendor's interrupt moderation mechanism.
  It seems RTL8169/RTL8168/RTL810xE has a kind of interrupt
  moderation mechanism but it is not documented at all. The magic
  value dramatically reduced number of interrupts without noticeable
  performance drops so apply it to all RTL8169/RTL8169 controllers.
  Vendor's FreeBSD driver also applies it to RTL810xE controllers but
  their Linux driver explicitly cleared the register, so do not
  enable interrupt moderation for RTL810xE controllers.

  While I'm here sort 8169 specific registers.

  Obtained from:	RealTek FreeBSD driver

MFC r215025:
  Only moderate TX completion interrupts. Relying on taskqueue to
  suppress RX interrupts seems to give better RX performance than
  RX interrupt moderation.

git-svn-id: svn://svn.freebsd.org/base/stable/8@215405 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f