The combination of 8740528b24
("Windows-compatible sentinel socket type and value") and
d497d7e4a7 ("krb5_sendto_kdc:
failover for multiple AAAA/A RRs on one domain") broke
all the send to kdc loop on Windows. rk_socket_t is
a HANDLE and rk_INVALID_SOCKET is the max value. Therefore,
no valid socket will be larger and all communications
will fail.
Change-Id: I3464f78d67b19f14050ad7a01738fb32bac99385
a1276c54aa