fix for getaddrinfo problem on Compaq Tru64 UNIX

[Robert Urban]

Hello OpenSSH Developers,

Tru64 V5.1, and probably previous versions, assumes you want 4.3BSD socket
behaviour unless 4.4BSD sockets are explicitly requested, which can
be done by #defining one of "_SOCKADDR_LEN" or "_XOPEN_SOURCE_EXTENDED".
Probably #defining "_SOCKADDR_LEN" has less consequences.

4.3BSD socket behaviour means that getaddrinfo returns sockaddr structs
where sa_family is set to zero, which causes subsequent calls to
getnameinfo to barf.

Any chance you can take this into consideration in "configure"?

thanks,

Rob Urban