This enables building WolfSSL with Curve448, which can be used by
Strongswan. This has been tested on a Linksys E8450, running OpenWrt
22.03-rc4.
This allows parity with OpenSSL, which already supports Curve448 in
OpenWrt 21.02.
Fixesopenwrt/packages#18812.
Signed-off-by: Joel Low <joel@joelsplace.sg>