Precise ephemeris can be provided as file

In RTKNAVI and RTKRCV, precise ephemeris can be provided by direct download from a FTP or HTTP server but cannot be provided as a File.

This is due to a specific behavior. A file is transmit to the core as an "emulated" stream. So svr->buff[index] is a paging buffer containing one page of the file. After the reading next page is filled in the buffer etc. .
A 'FTP' stream type is different, when started the core download the remote file, uncompress it and transmit the path of the temporary file to readsp3(..) this function open it and parse it.

I've made a change in decodefile(...) for treating the "FILE" stream type as a file and not as a pseudo stream for format STRFMT_SP3, because I'm not sure that a SP3 can be streamed. I think that because there is a single header.

This is a workaround only since it lacks one feature: it cannot re-parse the file if this one change.