net: lwm2m: Fix socket offload and native TLS conflict

Removed auto select from LWM2M_DTLS_SUPPORT
* TLS_CREDENTIALS
* NET_SOCKETS_SOCKOPT_TLS
* NET_SOCKETS_ENABLE_DTLS

LwM2M stack shouldn't enforce these options as they
are not needed with socket offloading.

Signed-off-by: Juha Heiskanen <juha.heiskanen@nordicsemi.no>