This option enables using sendfile() in ftpc binary transfer mode of PUT operation.
If the option is enabled but ASCII transfer mode is activated,
ftpc falls back to the combination of read() and write().
Using sendfile() provides a higher performance compared to
the combination of read() and write().
Also this option is useful for testing / debugging tcp_sendfile()
functionality of NuttX TCP/IP stack.
FTP: Adds support for IPv6 and fixes various transfer issues
* netutils/ftpd: Fix support for IPv6 FTP server
* netutils/ftpc:Adds support for IPv6 sockets
* ftpc: Must convert port received by EPSV reply to network order
* ftpc: Data socket address for passive connection should be same as server address
* ftpc: Must skip human readable string in EPSV response before scanning for port
* ftpc: Don't send PASS command if USER command was sufficient. ie no password required
* ftpc: Generically handle permanent negative completion in shard ftpc_cmd logic
* ftpc: Minor addresssing fix
* ftpc: Tweak logic for overriding network debugging output
* FTP: Adds option for setting stack size of various threads in FTPD and FTPC
* netutils/ftpd: Fixes build error setting IPv4 address. sin_addr => sin_addr.s_addr
* netutils/ftpd: Protects against partial write returns by looping in that case
Approved-by: Gregory Nutt <gnutt@nuttx.org>
