dropbear: add ECDSA support

Be aware that if you don't want your RSA and DSS host keys to be re-generated, you should execute the command {{{dropbearkey -t ecdsa -f /tmp/flash/dropbear/ecdsa_host_key}}} and {{{modsave flash}}} before flashing the new FW.



git-svn-id: file:///var/svn/freetz/trunk@12210 149334a1-2f27-0410-a3b9-fc62619ac1e6