doc: fix checking socket() in net tstamp example

Signed-off-by: NAli Gholami Rudi <ali@rudi.ir>
Acked-by: NPatrick Ohly <patrick.ohly@intel.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Documentation/networking/timestamping/timestamping.c

@@ -370,7 +370,7 @@ int main(int argc, char **argv)
 	}
 
 	sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
-	if (socket < 0)
+	if (sock < 0)
 		bail("socket");
 
 	memset(&device, 0, sizeof(device));