Right. you have to upgrade CE to 2.4.3-p1. I don't think this info has been refreshed on the new forum yet. There are other threads on it.
Here are the basics for what you need to do for the PV NICs:
Install it, shut it down. Add the NICs you want, then in XenServer:
Get the VM's uuid
# xe vm-list name-label="pfSense B" | grep "^uuid" | awk '{print $NF}'
43fdd0da-73ca-22c0-97f6-0ac47ae82360
Get the UUIDs for the NICs
# xe vif-list vm-uuid="43fdd0da-73ca-22c0-97f6-0ac47ae82360" | grep "^uuid" | awk '{print $NF}'
6c9cb724-705a-0449-2176-505dd332431d
a4c4ec8f-de68-eab3-69c7-d5b6c8be7b53
25e0d1b6-6d9a-6480-4612-e5aca876a922
71919d5a-000c-b9b3-31ed-21fa1674ba4e
1bf1eaf3-50fe-4a12-c3fa-1341766cee08
7b50e7fd-d6ec-598d-8dd6-6068d5f2765b
Turn off the checksum checking in the NICs. Run this for all of them:
# xe vif-param-set uuid=6c9cb724-705a-0449-2176-505dd332431d other-config:ethtool-tx="off"
Boot the VM and the traffic in should flow through fine on the PV NICs.
The other major caveat is the HV NICs (reX) support altq shaping. The PV NICs (xnX) don't.