Tone down the Nsock trace level with --packet-trace, --version-trace,

and --script-trace. It was set at 5, now it's 2. That's enough to see
all the Nsock events and the contents of reads and writes. At 3 you
start to get messages like
	PCAP do_actual_pcap_read READ (IOD #%li) (EID #%li) size=%i
The message "wait_for_events" isn't printed until level 4. Getting rid
of that is the main reason for this change.

nmap.h

@@ -288,6 +288,9 @@ void *realloc();
 
 #define MAXFALLBACKS 20 /* How many comma separated fallbacks are allowed in the service-probes file? */
 
+/* The trace level to give to nsp_settrace with --packet-trace et al. */
+#define NSOCK_TRACE_LEVEL 2
+
 /* Default maximum send delay between probes to the same host */
 #ifndef MAX_TCP_SCAN_DELAY
 #define MAX_TCP_SCAN_DELAY 1000