lws_plat_fd introduce struct
lws_plat_fd introduce struct

Originally from

https://github.com/warmcat/libwebsockets/pull/363

Modified by AG to change the emphasis to exporting lws plat
handlers for use by the user code portably
sartura/libwebsockets,dumganhar/libwebsockets,dumganhar/libwebsockets,ralight/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,ralight/libwebsockets,sartura/libwebsockets,dumganhar/libwebsockets,sartura/libwebsockets,dumganhar/libwebsockets,sartura/libwebsockets,ralight/libwebsockets,sartura/libwebsockets,ralight/libwebsockets,ralight/libwebsockets,dumganhar/libwebsockets