netfilter: ebtables: allow xtables-nft only builds

Same patch as previous one, but for ebtables.

To build a kernel that only supports ebtables-nft, the builtin tables
need to be disabled, i.e.:

CONFIG_BRIDGE_EBT_BROUTE=n
CONFIG_BRIDGE_EBT_T_FILTER=n
CONFIG_BRIDGE_EBT_T_NAT=n

The ebtables specific extensions can then be used nftables'
NFT_COMPAT interface.
Signed-off-by: Florian Westphal <fw@strlen.de>

net/bridge/netfilter/Kconfig

@@ -39,6 +39,10 @@ config NF_CONNTRACK_BRIDGE
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+# old sockopt interface and eval loop
+config BRIDGE_NF_EBTABLES_LEGACY
+	tristate
+
 menuconfig BRIDGE_NF_EBTABLES
 	tristate "Ethernet Bridge tables (ebtables) support"
 	depends on BRIDGE && NETFILTER && NETFILTER_XTABLES
@@ -55,6 +59,7 @@ if BRIDGE_NF_EBTABLES
 #
 config BRIDGE_EBT_BROUTE
 	tristate "ebt: broute table support"
+	select BRIDGE_NF_EBTABLES_LEGACY
 	help
 	  The ebtables broute table is used to define rules that decide between
 	  bridging and routing frames, giving Linux the functionality of a
@@ -65,6 +70,7 @@ config BRIDGE_EBT_BROUTE
 
 config BRIDGE_EBT_T_FILTER
 	tristate "ebt: filter table support"
+	select BRIDGE_NF_EBTABLES_LEGACY
 	help
 	  The ebtables filter table is used to define frame filtering rules at
 	  local input, forwarding and local output. See the man page for
@@ -74,6 +80,7 @@ config BRIDGE_EBT_T_FILTER
 
 config BRIDGE_EBT_T_NAT
 	tristate "ebt: nat table support"
+	select BRIDGE_NF_EBTABLES_LEGACY
 	help
 	  The ebtables nat table is used to define rules that alter the MAC
 	  source address (MAC SNAT) or the MAC destination address (MAC DNAT).

net/bridge/netfilter/Makefile

@@ -9,7 +9,7 @@ obj-$(CONFIG_NFT_BRIDGE_REJECT)  += nft_reject_bridge.o
 # connection tracking
 obj-$(CONFIG_NF_CONNTRACK_BRIDGE) += nf_conntrack_bridge.o
 
-obj-$(CONFIG_BRIDGE_NF_EBTABLES) += ebtables.o
+obj-$(CONFIG_BRIDGE_NF_EBTABLES_LEGACY) += ebtables.o
 
 # tables
 obj-$(CONFIG_BRIDGE_EBT_BROUTE) += ebtable_broute.o