[NETFILTER]: ebtables: Update modules' descriptions

Update the MODULES_DESCRIPTION() tags for all Ebtables modules.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>