MFC r227311-227312,227318-227319,227322-227324:

MFC r227311-227312,227318-227319,227322-227324:
r227311:
  Remove ti_unit member variable in softc.
  While I'm here use PCIR_BAR macro.

r227312:
   o Remove unnecessary controller reinitialization.
   o Do not blindly UP controller when MTU is changed. Reinitialize
     controller only if driver is running.
   o Remove useless ti_stop() in ti_watchdog() since ti_init_locked()
     always invokes ti_stop().

r227318:
  Track which ring was updated in RX handler and update only modified
  ring. This should reduce unnecessary register accesses.

r227319:
  Mini ring is not available on Tigon 1 so do not create DMA maps for
  mini ring on Tigon 1 to save resources.

r227322:
  Show RX buffer allocation failure and do not blindly send alive
  message to firmware. Probably the correct way for this error is to
  send a TI_CMD_CODE_STACK_DOWN message to firmware and let firmware
  handle the rest.

r227323:
  If ti_chipinit() fails in ti_stop(), ignore the error and release
  all allocated TX/RX buffer resources. If the interface is brought
  to up again after the error, we will leak allocated TX/RX buffers.

r227324:
  Do not allow changing MTU to be less than the minimum.

git-svn-id: svn://svn.freebsd.org/base/stable/8@229422 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f