MFC: if_dc.c rev1.57

MFC: if_dc.c rev1.57
  - In dc_intr(), check IFF_RUNNING instead of IFF_UP; this closes a possible
    time window between IFF_UP is set but not IFF_RUNNING.
  - In dc_ioctl(), don't program multicast filter, if NIC is not running yet.
    Add assertion in Xircom's multicast filter programming function to make
    sure that NIC is running.
  - Don't set IFF_RUNNING in Xircom's multicast filter programming function.
  - Move setting IFF_RUNNING before programming multicast filter; just to keep
    the IFF_RUNNING assertion work.  Add comment about it

  Dragonfly-bug: <http://bugs.dragonflybsd.org/issue1106>
  Tested-by: Tim <t-df@timdarby.net>