dhcpcd: Add arpgw command line flag

We added a configuration file flag for this feature in
http://gerrit.chromium.org/gerrit/3080 ; now make the
command line flag accessible.

BUG=chromium-os:16885
TEST=Manual -- use new flimflam set-arp-gateway command to turn on
arpgw, ensure dhcpcd starts up, shows command line flag in "ps" listing
and that /var/log/messages shows that it actually arped successfully for
its gateway.

Change-Id: I8e3ba4bf8e327a29e76a689c024c2ea7267ed552
Reviewed-on: http://gerrit.chromium.org/gerrit/3531
Reviewed-by: Sam Leffler <sleffler@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
1 file changed