I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG. These comments were written primarily for the benefit of the
security area directors. Document editors and WG chairs should treat
these comments just like any other last call comments.

The summary of the review is the document has minor issue.

The document is well written and fairly simple.  Referencing the previous security considerations does provide some good advice, but it seems that this document perhaps adds some considerations about the size of BPDU packets.  It seems that it would be possible for excessively large packets could cause problems for the sender or receiver.  Perhaps add something to the security considerations about: 
Implementations should consider this and set appropriate upper bounds on amount of padding added to these messages and on the length of received messages.