Portability fix for commit 9a895462d.

So far as I can find, NI_MAXHOST isn't actually required anywhere by
POSIX.  Nonetheless, commit 9a895462d supposed that it could rely on
having that symbol without any ceremony at all.  We do have a hack
for providing it if the platform doesn't, in getaddrinfo.h, so fix
the problem by #including that file.  Per buildfarm.

src/include/replication/walreceiver.h

@@ -15,6 +15,7 @@
 #include "access/xlog.h"
 #include "access/xlogdefs.h"
 #include "fmgr.h"
+#include "getaddrinfo.h"		/* for NI_MAXHOST */
 #include "replication/logicalproto.h"
 #include "replication/walsender.h"
 #include "storage/latch.h"