User-space networking stack API allows user-space daemon to
provide TCP/IP stack implementation for NuttX network.
Main use for this is to allow use and seamless integration of
HW-provided TCP/IP stacks to NuttX.
For example, user-space daemon can translate /dev/usrsock
API requests to HW TCP/IP API requests while rest of the
user-space can access standard socket API, with socket
descriptors that can be used with NuttX system calls.
For the setsockopt() case, it will always use the final option. This means that a time of zero (i.e., not timeout) can only occur if the value zero was explicated provided to setsockopt().
