package/libnetconf2: add patch to fix incompatiblity with libssh

package/libnetconf2: add patch to fix incompatiblity with libssh

The libnetconf2 upstream project rejects building with ssh support for
libssh 0.9.3 and 0.9.4 due to an existing regression.

This libssh regression bug is already fixed upstream. The libssh buildroot
package has the patch (39099153d9404cd6f107f0fd92ce8686bbd1beb2).

Thus we can remove the libnetconf2 cmake check.

Fixes:
http://autobuild.buildroot.net/results/f72fcccafe70ecb6b2ba21e8d19c5827a09ffec7/

Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>