So I set an L2 firewall rule on a 2.4Ghz ePMP 1000 GPS Sync AP in bridge mode.
Name: Log PPPoE Descovery
Action: Accept
Interface: WLAN
Log: ON
EtherType: 8863
Customer radios are configured to NAT/DHCP and PPPoE Enabled so I was thinking this rule should cause the AP to log whenever a connected radio sends a PPPoE descovery packet however it does not appear to be doing that.