When resolving the "constraint" (singular), store all returned IP

When resolving the "constraint" (singular), store all returned IP
addresses and try one after another until the connection succeeded -
based on the existing mechanism of "server".  "constraint" previously
only tried to connect to the first returned address, aborted and
skipped the constraint on failure.  In difference to "constraints"
(plural), it still only connects to one address at a time and not to
all of them at once.

Pointed out by rpe@
OK rpe@ deraadt@