krb5_sendto_kdc: Windows no KDC reachable error
The combination of
8740528b2477f872147998ca19a66d2fae12631b
("Windows-compatible sentinel socket type and value") and
d497d7e4a796c6bda153e7f10fe9478724b855ab ("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