Fix building OVS on ppc64le and armv7hl

Python 3.9 changed the architecture naming in suffix used for binary
extensions.
Use python3-config --extension-suffix in order to figure out the correct
extension suffix used for binary extensions.

openvswitch.spec

@@ -264,7 +264,7 @@ export CPPFLAGS="-I ../include"
 export LDFLAGS="%{__global_ldflags} -L $RPM_BUILD_ROOT%{_libdir}"
 %py3_build
 %py3_install
-[ -f "$RPM_BUILD_ROOT/%{python3_sitearch}/ovs/_json.cpython-%{python3_version_nodots}$(python3-config --abiflags)-%{_arch}-%{_target_os}%{?_gnu}.so" ]
+[ -f "$RPM_BUILD_ROOT/%{python3_sitearch}/ovs/_json$(python3-config --extension-suffix)" ]
 )
 popd