Make default lag-in-frames=19

The earlier default was 25, which was reduced to 17 in
https://aomedia-review.googlesource.com/c/aom/+/28181

However, as temporal filtering may use 3 frames on either side by
default, we should have default lag in frames as 16 + 3 = 19.

The compression performance is exactly neutral between lag-in-frames of
25 and 17.

Change-Id: I5603f899183a0363eb4c9160a6cacc4e68585725

av1/av1_cx_iface.c

diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index 106e2c0..9eef662 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -1616,7 +1616,7 @@
 
         AOM_RC_ONE_PASS,  // g_pass
 
-        17,  // g_lag_in_frames
+        19,  // g_lag_in_frames
 
         0,                // rc_dropframe_thresh
         RESIZE_NONE,      // rc_resize_mode