libs/wolfssl: disable hardening check in `settings.h`

libs/wolfssl: disable hardening check in `settings.h`

This seems to cause a false-positive warning/error
while building `libwebsockets-cyassl`.

```
make[6]: Leaving directory '/home/sandu/work/lede/build_dir/target-x86_64_musl/libwebsockets-cyassl/libwebsockets-2.2.1'
make[6]: Entering directory '/home/sandu/work/lede/build_dir/target-x86_64_musl/libwebsockets-cyassl/libwebsockets-2.2.1'
[  2%] Building C object CMakeFiles/websockets.dir/lib/base64-decode.c.o
In file included from /home/sandu/work/lede/staging_dir/target-x86_64_musl/usr/include/wolfssl/ssl.h:31:0,
                 from /home/sandu/work/lede/staging_dir/target-x86_64_musl/usr/include/cyassl/ssl.h:33,
                 from /home/sandu/work/lede/staging_dir/target-x86_64_musl/usr/include/cyassl/openssl/ssl.h:30,
                 from /home/sandu/work/lede/build_dir/target-x86_64_musl/libwebsockets-cyassl/libwebsockets-2.2.1/lib/private-libwebsockets.h:256,
                 from /home/sandu/work/lede/build_dir/target-x86_64_musl/libwebsockets-cyassl/libwebsockets-2.2.1/lib/base64-decode.c:43:
/home/sandu/work/lede/staging_dir/target-x86_64_musl/usr/include/wolfssl/wolfcrypt/settings.h:1642:14: error: #warning "For timing resistance / side-channel attack prevention consider using harden options" [-Werror=cpp]
             #warning "For timing resistance / side-channel attack prevention consider using harden options"

```

Hardening is enabled by default in libwolfssl at build-time.

However, the `settings.h` header is exported (along with other headers)
for build (via Build/InstallDev).

This looks like a small bug/issue with wolfssl.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>