fixed JSON output

src/dp_events.c

 			fprintf(fh, "\"abs\": %llu }", stats4->abscnt[i]);
 		}
 
-		if ( ( stats4->relcnt[i]>0 || stats4->abscnt[i]>0 ) && i-1 != DP_DHCPV4_CODE_LEN )
+		if ( ( stats4->relcnt[i]>0 || stats4->abscnt[i]>0 ) && i+1 != DP_DHCPV4_CODE_LEN )
 			fprintf(fh, ", ");
 
 		stats4->relcnt[i]=0;
 			fprintf(fh, "\"abs\": %llu }", stats6->abscnt[i]);
 		}
 
-		if ( ( stats6->relcnt[i]>0 || stats6->abscnt[i]>0 ) && i-1 != DP_DHCPV6_CODE_LEN )
+		if ( ( stats6->relcnt[i]>0 || stats6->abscnt[i]>0 ) && i+1 != DP_DHCPV6_CODE_LEN )
 			fprintf(fh, ", ");
 
 		stats6->relcnt[i]=0;