Wrong signature for mocked function

In logging_test.c we mock "sendto" to avoid sending data. In HPUX the compiler
is a little bit more strict than anticipated so it was complaining about the
type of the signature. It is interesting that this worked all over the place
and no other compiler complained even though it is evidently a failure.
Merge pull request #669 from cduclos/master

Fixing an evident compilation failure