wolfssl: always export wc_ecc_set_rng

wolfssl: always export wc_ecc_set_rng

Since commit 6467de5a8840 ("Randomize z ordinates in scalar
mult when timing resistant") wolfssl requires a RNG for an EC
key when the hardened built option is selected.

wc_ecc_set_rng is only available when built hardened, so there
is no safe way to install the RNG to the key regardless whether
or not wolfssl is compiled hardened.

Always export wc_ecc_set_rng so tools such as hostapd can install
RNG regardless of the built settings for wolfssl.

Signed-off-by: David Bauer <mail@david-bauer.net>