9322 Print stats since boot for first line of arcstat.pl

Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

usr/src/cmd/stat/arcstat/arcstat.pl

@@ -166,8 +166,11 @@ sub init {
 	detailed_usage() if $vflag;
 	@hdr = @xhdr if $xflag;		#reset headers to xhdr
 
-	# check if L2ARC exists
+	# we want to capture the stats here, so that we can use them to check
+	# if an L2ARC device exists; but more importantly, so that we print
+	# the stats since boot as the first line of output from main().
 	snap_stats();
+
 	if (defined $cur{"l2_size"}) {
 		$l2exist = 1;
 	}
@@ -353,12 +356,12 @@ sub main {
 	if ($count > 0) { $count_flag = 1; }
 	while (1) {
 		print_header() if ($i == 0);
-		snap_stats();
 		calculate();
 		print_values();
 		last if ($count_flag == 1 && $count-- <= 1);
 		$i = (($i == $hdr_intr) && (not $raw_output)) ? 0 : $i+1;
 		sleep($int);
+		snap_stats();
 	}
 	close($out) if defined $out;
 }