Function silc_sftp_write
SYNOPSIS
void silc_sftp_write(SilcSFTP sftp,
SilcSFTPHandle handle,
uint64 offset,
const unsigned char *data,
uint32 data_len,
SilcSFTPStatusCallback callback,
void *context);
DESCRIPTION
Writes to a file indicated by the file handle `handle' starting from
offset of `offset' at most `data_len' bytes of `data'. The `callback'
is called to indicate the status of the writing.