Netmap is not likely to play very well with a transparent firewall bridge setup, especially with the way netmap is currently implemented within Suricata. Some improvements are planned upstream for netmap, but there is not yet a timetable for their release.
Also note that Suricata will not work properly with a PPPoE type interface. I mention that because that is a popular type of setup for a WAN. The most popular is DHCP, but there are lots of PPPoE connections. The least popular setup is a static IP on the WAN.
If you want to continue with the transparent firewall arrangement, I recommend you use Legacy Mode blocking.