There is an `typdef void sock_udp_ep_t` hack in `nanocoap.h` that tries
allow using parts of nanocoap without a RIOT network stack.
There is a similar hack to allow it to be used without RIOT at all. This
has been used in the early days during development on Linux directly.
This however has not been tested and left bit rotting.
Both hacks are remove and nanocoap now just depends on sock/udp.h.
In a future cleanup, the CoAP packet parsing and building code of
nanocoap can be separated from the part that does the transmission and
reception of UDP packets. That way, using nanocoap's packet parsing and
building will again be available without using a network stack.
Until then, let's drop the hacks and just depend on a network stack.
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