Add op index support for custom hooks

src/python/grpcio/grpc/_cython/_cygrpc/_hooks.pxd.pxi

@@ -13,4 +13,4 @@
 # limitations under the License.
 
 
-cdef object _custom_op_on_c_call(grpc_call *call)
+cdef object _custom_op_on_c_call(int op, grpc_call *call)

src/python/grpcio/grpc/_cython/_cygrpc/_hooks.pyx.pxi

@@ -13,5 +13,5 @@
 # limitations under the License.
 
 
-cdef object _custom_op_on_c_call(grpc_call *call):
-  return None
+cdef object _custom_op_on_c_call(int op, grpc_call *call):
+  raise NotImplementedError("No custom hooks are implemented")

src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi

@@ -94,5 +94,5 @@ cdef class Call:
   def is_valid(self):
     return self.c_call != NULL
 
-  def _custom_op_on_c_call(self):
-    return _custom_op_on_c_call(self.c_call)
+  def _custom_op_on_c_call(self, int op):
+    return _custom_op_on_c_call(op, self.c_call)