This avoids multiple config file entries for the same interface
causing an assertion failure.  Reported by Baptiste Jonglez.

Conflicts:
	CHANGES

It turns out that the rp_filter is only disabled if both all/rp_filter
and ifname/rp_filter are set to 0.  This sets and restores all of these
values explicitly, which fixes mysterious issues on distributions that
set rp_filter by default.

This avoids a crash when an interface is added both in the configuration
file and on the command-line.

This was causing the parser to ignore the rest of the file after an
unknown option.

This avoids various unpleasant edge-cases.

This probably ensures that everything that can be done from the
command-line can be done from the configuration file.

This also adds options protocol-port and protocol-group.

This was causing the channel list to remain stuck at the old value
when we were rerouting.