Provide a complete documentation guide for the tftpc (TFTP client) network
utility in Documentation/applications/netutils/tftpc/index.rst, replacing
the previous 5-line placeholder stub.
Includes:
- Architecture overview (NSH get/put engine + programmatic C APIs)
- Key features (RFC 1350, octet/netascii modes, streaming callbacks, dynamic TID port negotiation)
- Configuration options table and networking prerequisites
- NSH get and put command synopses, option flags, and terminal examples
- C API reference for filesystem helpers (tftpget, tftpput) and streaming callbacks (tftpget_cb, tftpput_cb)
- Complete, runnable C application example demonstrating callback-based streaming downloads
Addresses #11081
Signed-off-by: Swatantra Yadav <maverickswatantra@gmail.com>
5b597668f0