ANK's patch changed behavior of the '-i <device>' option. Without this
option tcpdump listens on *all* devices, and not on the lowest numbered one
as the man-page says:
| -i Listen on interface. If unspecified, tcpdump searches the
| list for the lowest numbered,
True. The documentation refers to the old behaviour (which can now
used with -R).
Err, -R requires you give -i.