selftests: net: tls: check if FIPS mode is enabled

TLS selftests use the ChaCha20-Poly1305 and SM4 algorithms, which are not
FIPS compliant. When fips=1, this set of tests fails. Add a check and only
run these tests if not in FIPS mode.

Fixes: 4f336e88 ("selftests/tls: add CHACHA20-POLY1305 to tls selftests")
Fixes: e506342a ("selftests/tls: add SM4 GCM/CCM to tls selftests")
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Magali Lemes <magali.lemes@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>