The `coap_socket_t` and `coap_socket_type_t` types are used by gCoAP
only and the `coap_` prefix is usually used to namespace the `nanocoap`
module's API. This makes it confusing to locate the types in question.
Signed-off-by: Martine Lenders <m.lenders@fu-berlin.de>
4b7ef70e66