KEEPALIVED_INTERFACE - default to default gw interface

[ReSearchITEng]

KEEPALIVED_INTERFACE instead of eth0, can you default to the default gw one?
$(ip route | grep default | head -1 | cut -d" " -f5)

I think this would cover most of the cases.

So the environment variable of this network card name still cannot be overridden by the user, right?