package/ebtables: install symlink to ebtables-legacy

Since the upgrade of ebtables from 2.0.10-4 to 2.0.11, there no longer is an
'ebtables' binary. It has been renamed to 'ebtables-legacy' and moved from
'/sbin' to '/usr/sbin'. This change is part of the upstream change to
integrate the functionality of ebtables (and arptables) in the iptables
package, using the nf_tables kernel backend [1].

Unfortunately, the renaming (and move) of the original 'ebtables' binary
breaks existing scripts that are calling 'ebtables' or '/sbin/ebtables'.
Therefore, add a symlink from the original path to 'ebtables-legacy'.

However, do not provide this symlink if BR2_PACKAGE_IPTABLES_NFTABLES is
enabled. In this case, the iptables package will build the new equivalent
of ebtables -- a symlink to ebtables-legacy would cause conflicts.

[1] https://wiki.nftables.org/wiki-nftables/index.php/Legacy_xtables_tools



Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Acked-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>