This is a security fix and applies to all architectures.
Quote from the commit message:
"Minimum IP MTU" means what it says. Ensure that packets returned by dhcpd are the minimum size or larger no matter what the client thinks the minimum allowable size is. Found by Nahuel Riva and Gera Richarte.
Fix by millert@.
Binpatches exist for OpenBSD 4.1 and OpenBSD 4.0.