fix(tf): make se_atten_v2 masking smooth when davg is not zero (#3632)

Currently, `se_atten_v2` is always masked to zero when `exclude_types`
is given. However, for the no neighbor case, the placeholder for a
virtual neighbor is `davg`. This causes discontinuity when
`set_davg_zero` is not set.

This PR uses `davg` for masking.

In production, we usually use `set_davg_zero` along with
`exclude_types`, so it hasn't caused a real problem.

I notice PT hasn't implemented `se_atten_v2` or `exclude_types`, but we
need attention in the future.

---------

Signed-off-by: Jinzhe Zeng <jinzhe.zeng@rutgers.edu>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

deepmd/tf/descriptor/se_atten.py

@@ -681,7 +681,17 @@ def _pass_filter(
                 tf.shape(inputs_i)[0],
                 self.nei_type_vec,  # extra input for atten
             )
-            inputs_i *= mask
+            if self.smooth:
+                inputs_i = tf.where(
+                    tf.cast(mask, tf.bool),
+                    inputs_i,
+                    # (nframes * nloc, 1) -> (nframes * nloc, ndescrpt)
+                    tf.tile(
+                        tf.reshape(self.avg_looked_up, [-1, 1]), [1, self.ndescrpt]
+                    ),
+                )
+            else:
+                inputs_i *= mask
         if nvnmd_cfg.enable and nvnmd_cfg.quantize_descriptor:
             inputs_i = descrpt2r4(inputs_i, atype)
         layer, qmat = self._filter(