ncftp: use tar.gz to workaround upstream changing tarball post-release

ncftp: use tar.gz to workaround upstream changing tarball post-release

As explained here:
http://lists.busybox.net/pipermail/buildroot/2017-March/185550.html

Upstream has silently updated their 3.2.6 tarball some time between our
version bump in late November and December 4th.  The changed tarball also
contains a significant amount of source changes:

 libncftp/c_opennologin.c  |    4
 libncftp/ftp.c            |   31
 libncftp/ftw.c            |    2
 libncftp/io_getmem.c      |    2
 libncftp/io_list.c        |    6
 libncftp/io_sendfile.c    |    4
 libncftp/io_util.c        |    4
 libncftp/ncftp.h          |    2
 libncftp/open.c           |    4
 libncftp/rftw.c           |    2
 libncftp/rglobr.c         |    2
 libncftp/u_decodehost.c   |    2
 libncftp/u_decodeurl.c    |    2
 libncftp/u_getpass.c      |    2
 libncftp/u_misc.c         |    2
 libncftp/u_pathcat.c      |    4
 libncftp/u_scram.c        |    2
 libncftp/wincfg.h         |    1
 ncftp/cmds.c              |   38 -
 ncftp/gl_getline.c        |   26
 ncftp/ls.c                |    9
 ncftp/ls.h                |    9
 ncftp/progress.c          |    9
 ncftp/readln.c            |    4
 ncftp/shell.h             |   10
 ncftp/spoolutil.c         |    8
 ncftp/version.c           |    2
 sh/mksrctar.sh            |    1
 sh_util/gpshare.c         |   12
 sh_util/ncftpbatch.c      |  110 --
 sh_util/ncftpget.c        |    6
 sh_util/ncftpls.c         |    5
 sh_util/ncftpput.c        |   14
 sio/DNSUtil.c             |    4
 sio/Makefile.in           |   16
 sio/SBind.c               |   35
 sio/SConnect.c            |    9
 sio/SNew.c                |  115 ---
 sio/SRead.c               |    6
 sio/StrAddr.c             |    6
 sio/config.h.in           |   24
 sio/configure.in          |    8
 sio/sio.h                 |   18
 sio/wincfg.h              |    1
 vis/bmed.c                |   13
 vis/wgets.c               |   12
 vis/wgets.h               |    7
 vis/wutil.c               |    6
 vis/wutil.h               |    6

Upstream has been contacted to verify if this change was intentional and the
reason why. From the mail:

> Is this update intentional? Why was the tarball regenerated?

Yes.

The old hash was unfortunately already used in the 2017.02 (and .1)
releases, so just changing the hash and updating the tarball on
sources.buildroot.org would break ncftp for users of those releases.
Instead change to use the .tar.gz tarball as suggested by Arnout.

Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>