openvswitch: openvswitch.mk: add ovs_common_depends variable

This is to address the need that openvswitch starting with 2.13 now
depends on libunwind for handling SIGSEGV (upstream commit e2ed6fbeb18
("fatal-signal: Catch SIGSEGV and print backtrace"))

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

net/openvswitch/openvswitch.mk

@@ -10,6 +10,7 @@ ovs_builddir=$(KERNEL_BUILD_DIR)/openvswitch-$(ovs_version)
 
 # Shared vars, macros
 
+ovs_common_depends:=
 ovs_packages:=
 
 ovs_package_name=$(if $(filter openvswitch,$(1)),openvswitch,openvswitch-$(1))
@@ -21,7 +22,7 @@ define OvsPackageTemplate
      URL:=https://www.openvswitch.org
      TITLE:=$(ovs_$(1)_title)
      HIDDEN:=$(ovs_$(1)_hidden)
-     DEPENDS:=$(ovs_$(1)_depends) +libatomic +libunbound
+     DEPENDS:=$(ovs_$(1)_depends) $(ovs_common_depends)
   endef
 
   define Package/$(call ovs_package_name,$(1))/install