Move exported functions used in capabilityHelper.h from extern "C" to api.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

capnp/__init__.py

@@ -52,6 +52,8 @@ from .lib.capnp import (
     _write_message_to_fd,
     _write_packed_message_to_fd,
     _Promise as Promise,
+    _init_capnp_api,
 )
 
+_init_capnp_api()
 add_import_hook() # enable import hook by default