You are right, I had a crossed wire, I was confusing which earlier thread this thread had been hijacked from. I am straightened out now.
That message means the packet has been dropped by SPI (SPI is not the only SPI setting endpoint filtering plays in here too in a not terribly well defined way). Period.
Also, I realize it doesn't matter at this point but even if your modem is gigabit (I haven't seen one personally but hey anything is possible), your WAN pipe is not (20+ is way less than 100, and not on the same scale as 1000) and having gigabit on your modem is not a benefit in the slightest.
Regardless of where on your LAN the DIR is it's LAN ports are gigabit, however even that is a non-issue in your environment because you only have 1 gigabit device you are therefore getting zero benefit from gigabit. If you paid someone for that network layout and your criteria was making use of gigabit then you could have burned the money and at least gotten a little heat out of it, as such even that was lost.