[…]
CONFIG_TARGET_DEVICE_PACKAGES_ath79_generic_DEVICE_tplink_tl-wdr3600-v1="slh-misc-8m slh-misc-qos -libustream-wolfssl -wpad-basic -wpad-mini -wpad wpad-openssl -wpad-basic-wolfssl"
[…]
### WLAN support
CONFIG_PACKAGE_wpad=m
CONFIG_PACKAGE_wpad-basic=m
CONFIG_PACKAGE_wpad-mini=m
CONFIG_PACKAGE_wpad-openssl=m
CONFIG_PACKAGE_wpad-basic-wolfssl=m
CONFIG_PACKAGE_wpad-wolfssl=m
CONFIG_WPA_SUPPLICANT_INTERNAL=y
CONFIG_WPA_RFKILL_SUPPORT=y
### ustream
CONFIG_libustream-wolfssl=m
[…]
works for me (I'm not really happy about this procedure and consider adding a local patch reverting the wolfssl as default additions, but it does the job).