When changing IFCAP_TXCSUM for if_awg set/clear hw assist bits for CSUM_IP, CSUM_UDP, CSUM_TCP not just CSUM_IP.
The card cannot handle just tcp/udp checksums it can only calculate ip checksums or full checksums (ip and tcp/udp).
Also don't consider IFCAP_RXCSUM for setting clearing the bits.
The CSUM_ flags in hw assist bits are only relevant for the tx path.
The rx path already checks IFCAP_RXCSUM to know if to fill in the checksums calculated by the card.