Implement optional syslog logging using ordinary

bb_xx_msg calls, and convert networking/* to it.
The rest of bbox will be converted gradually.

libbb/xfuncs.c

@@ -397,7 +397,7 @@ char *xasprintf(const char *format, ...)
 	va_end(p);
 #endif
 
-	if (r < 0) bb_perror_msg_and_die("xasprintf");
+	if (r < 0) bb_error_msg_and_die(bb_msg_memory_exhausted);
 	return string_ptr;
 }
 #endif