keep tx3g{Buffer,Size,Filled} in sync

wasn't clearing size/filled when we cleared buffer.

Bug: 151159638
Test: poc, but it didn't fail either before or after the patch
(cherry picked from commit f2acb7a0185cac34a1a688416879eda26ead4b14)

Change-Id: Ie62c28c0b91a1ec36ba1a307fea5ff73d5c085bf
1 file changed