[BUILD] fix 2 minor issues on AIX

AIX does not know about MSG_DONTWAIT. Fortunately, nearly all sockets
are already set to O_NONBLOCK, so it's not even required to change the
code.  It was only necessary to add this fcntl to the log socket which
lacked it.  The MSG_DONTWAIT value has been defined to zero when unset
in order to make the code cleaner and more portable.

Also, on AIX, "hz" is defined, which causes a problem with one function
parameter in time.c. It's enough to rename the parameter there. Last,
fix a missing #include <string.h> in proxy.c.
diff --git a/include/common/time.h b/include/common/time.h
index ced4b6b..2a4a142 100644
--- a/include/common/time.h
+++ b/include/common/time.h
@@ -485,7 +485,7 @@
         tv1;                       \
 })
 
-char *human_time(int t, short hz);
+char *human_time(int t, short hz_div);
 
 #endif /* _COMMON_TIME_H */