insertstream uses an error code from the reserved client range

The insertstream filter (deprecated in 22.08 and removed in 23.02) uses an error code (number 2003) from the reserved client error range that's between 2000 and 2999. The filter should instead use a more suitable error like ER_NON_INSERTABLE_TABLE (1471).

This caused the insertstream.sh test to fail with a malformed packet error instead of the expected error packet.