doxygen is reporting a couple of errors

[jodh-intel]

I just ran doxygen on the source (just copy https://github.com/01org/cc-oci-runtime/blob/master/Doxyfile to the top-level for a quick test :) and it shows a couple of errors:

/home/james/go/src/github.com/clearcontainers/shim/src/shim.c:377: warning: argument 'header' of command @param is not found in the argument list of read_frame(struct cc_shim *shim)
/home/james/go/src/github.com/clearcontainers/shim/src/shim.c:265: warning: The following parameters of send_proxy_message(struct cc_shim *shim, uint8_t type, uint8_t opcode, const char *payload, size_t payload_len) are not documented:
  parameter 'payload_len'

Related to #54.