cnid_metad: fix tsockfd_create() return value on error

We ran into a case where the netatalk log grew at an extremely rapid
pace.  There was one message that kept repeating:

cnid_metad[2528] {usockfd.c:169} (E:CNID): error in accept: Socket
operation on non-socket

An strace showed pselect() getting called on stdin, rather than an
actual socket.  Looking at the code, I see that tsockfd_create() will
return 0 instead of -1 if the call to getaddrinfo() fails, which is
obviously wrong.

Reviewed-by: Ralph Boehme <slow@samba.org>