Milter-greylist

Hmmm... it seems that the two options are not identical (not
that it is fatal in the example I see): in the added headers,
the original {if_addr} displayed the MTA's address, like:
"not delayed by $mta_hostname $mta_ip"

With {client_addr} in its place, this displays the MTA host
name and, confusingly but not fatally, the sender's IP address.

So I guess my patch is not academically correct :)
I see the macro is also used in p0f; I wonder if the substitution
would break anything (worse than user reports) there?.. Did not
check further.

//Jim