[ovsp4rt] PrepareFdbTxVlanTableEntry truncates port_vlan to 8 bits

[ffoulkes]

The PrepareFdbTxVlanTableEntry function encodes the port_vlan input as a single byte.

• The input value (port_vlan in the port_vlan_entry struct) is an int.
• The parameter value (vlan_ptr in the remove_vlan_and_fwd action) is bit<24>.
• VLAN identifiers are bit<12>.
• The value that OvS assigns to port_vlan is the int vlan field in the xbundle struct. The comment states that the value of this field is -1=trunk port, else a 12-bit VLAN ID.

This appears to be an error.

• If it's not a bug, the code should contain a comment acknowledging the truncation and explaining why this is not an error.
• If it is a bug, it should be fixed. The unit test will also have to be updated.

Note

• Need to address both ES2K and DPDK variations.
• The unit test should expect, and test with, a 12-bit input value.