openvswitch: provide in-tree kmod builds

openvswitch: provide in-tree kmod builds

Open vSwitch 2.10 introduces meters support to the kernel datapath.  In
upstream Linux, the feature is only available since 4.15

This is mainly for make the newly introduced meter features in linux
kernel datapath more easily available

	root@OpenWrt:/# ovs-ofctl -OOpenFlow13 meter-features br0
	OFPST_METER_FEATURES reply (OF1.3) (xid=0x2):
	max_meter:4294967295 max_bands:1 max_color:0
	band_types: drop
	capabilities: kbps pktps burst stats
	root@OpenWrt:/#

Size comparison between in-tree and upstreamed modules are attached

	  2800 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-geneve-intree/lib/modules/4.14.67/vport-geneve.ko
	  2736 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-geneve/lib/modules/4.14.67/vport-geneve.ko
	  2596 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-gre-intree/lib/modules/4.14.67/vport-gre.ko
	  2536 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-gre/lib/modules/4.14.67/vport-gre.ko
	288320 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-intree/lib/modules/4.14.67/openvswitch.ko
	118984 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch/lib/modules/4.14.67/openvswitch.ko
	  2792 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-lisp-intree/lib/modules/4.14.67/vport-lisp.ko
	  2788 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-stt-intree/lib/modules/4.14.67/vport-stt.ko
	  3668 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-vxlan-intree/lib/modules/4.14.67/vport-vxlan.ko
	  3400 Sep  5 08:47 ipkg-mips_24kc/kmod-openvswitch-vxlan/lib/modules/4.14.67/vport-vxlan.ko

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>