I updated the dropbear url because it wasn't uploaded to network cache.
I kept an old version because :
 * our patches don't work anymore with the latest version.
 * the latest version (at the date of this commit, doesn't have an
   interesting changelog).
 * by laziness.

Replacing openssh buildout by dropbear one.

Adding my own dropbear patch which was submitted to
dropbear developpers.

Add ipv6 patch for dropbear

Took here :
<https://lists.openwrt.org/pipermail/openwrt-devel/2009-May/004299.html>

Minor: Dropbear buildout fine tuning

Linking dropbear with slapos zlib

Replacing openssh buildout by dropbear one.

Adding my own dropbear patch which was submitted to
dropbear developpers.

Add ipv6 patch for dropbear

Took here :
<https://lists.openwrt.org/pipermail/openwrt-devel/2009-May/004299.html>

Minor: Dropbear buildout fine tuning

Linking dropbear with slapos zlib