Implement optional syslog logging using ordinary

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

networking/udhcp/libbb_udhcp.h

@@ -22,7 +22,6 @@
 
 void udhcp_background(const char *pidfile);
 void udhcp_start_log_and_pid(const char *client_server, const char *pidfile);
-void udhcp_logging(int level, const char *fmt, ...);
 
 void udhcp_run_script(struct dhcpMessage *packet, const char *name);