utils: add nl_has_capability() function

Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>
utils: indicate capability NL_CAPABILITY_ROUTE_BUILD_MSG_SET_SCOPE

This capability indicates that libnl does no longer overwrites
the route scope in rtnl_route_build_msg(), as fixed by commit
85ec9c7ad80c60f4f619472f2bb9d9595da93b26.

Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>