Add information on process-forking for TCP connections to metrics.

Add the relevant information to the metrics and to the output of
dump_cache() (which is called when dnsmasq receives SIGUSR1).
Hence, users not collecting metrics will still be able to
troubleshoot with SIGUSR1. In addition to the current usage,
dump_cache() contains the information on the highest usage
since it was last called.

src/option.c

@@ -5855,6 +5855,7 @@ void read_opts(int argc, char **argv, char *compile_opts)
   daemon->randport_limit = 1;
   daemon->host_index = SRC_AH;
   daemon->max_procs = MAX_PROCS;
+  daemon->max_procs_used = 0;
   
   /* See comment above make_servers(). Optimises server-read code. */
   mark_servers(0);