For bge(4), dc(4), lge(4), ndis(4), nge(4), pcn(4), re(4), sis(4), sk(4), ti(4)

For bge(4), dc(4), lge(4), ndis(4), nge(4), pcn(4), re(4), sis(4), sk(4), ti(4)
- Do not start tx engine or set if_timer, if there is nothing to be sent
- Let if_watchdog() kick if_start().  This may avoid a possible race (in the
  future) between testing/setting if_timer and calling if_watchdog().  Only
  bge(4), re(4), sk(4) and ti(4) require this change.  The rest drivers
  affected by this commit already have this in place.

Discussed-with: joerg
Reviewed-by: joerg