package/opkg-utils: needs Python3 on the host

The 'opkg.py' script installed by host-opkg-utils has as shebang:
    #!/usr/bin/env python3

which may not be available on all host machines.
Add a potential dependency on host-python3 via BR2_PYTHON3_HOST_DEPENDENCY,
which will only add the host-python3 dependency if no python3 is already
available on the host.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/opkg-utils/opkg-utils.mk

@@ -10,6 +10,8 @@ OPKG_UTILS_SITE_METHOD = git
 OPKG_UTILS_LICENSE = GPL-2.0+
 OPKG_UTILS_LICENSE_FILES = COPYING
 
+HOST_OPKG_UTILS_DEPENDENCIES += $(BR2_PYTHON3_HOST_DEPENDENCY)
+
 define HOST_OPKG_UTILS_BUILD_CMDS
 	$(MAKE) -C $(@D) $(HOST_CONFIGURE_OPTS)
 endef