SessionID allocation issue

[xiangfeima]

This is a follow-up of #1424.
PR #1450, which fixed #1424, did not update the session id allocation process accordingly.
Because from #1450 rsp_session_id occupies the most-significant bytes of a whole session_id,
thus the req_session_id inside libspdm_allocate_req_session_id() should be caululated from 0xFFFF,
and rsp_session_id inside libspdm_allocate_rsp_session_id() should be caululated from 0xFFFF0000.

libspdm/library/spdm_requester_lib/libspdm_req_common.c

Lines 9 to 25 in bda8d7e

	uint16_t libspdm_allocate_req_session_id(libspdm_context_t *spdm_context)
	{
	uint16_t req_session_id;
	libspdm_session_info_t *session_info;
	size_t index;
	session_info = spdm_context->session_info;
	for (index = 0; index < LIBSPDM_MAX_SESSION_COUNT; index++) {
	if ((session_info[index].session_id & 0xFFFF0000) == (INVALID_SESSION_ID & 0xFFFF0000)) {
	req_session_id = (uint16_t)(0xFFFF - index);
	return req_session_id;
	}
	}
	LIBSPDM_DEBUG((LIBSPDM_DEBUG_ERROR, "libspdm_allocate_req_session_id - MAX session_id\n"));
	return (INVALID_SESSION_ID & 0xFFFF0000) >> 16;
	}

libspdm/library/spdm_responder_lib/libspdm_rsp_common.c

Lines 9 to 25 in bda8d7e

	uint16_t libspdm_allocate_rsp_session_id(const libspdm_context_t *spdm_context)
	{
	uint16_t rsp_session_id;
	const libspdm_session_info_t *session_info;
	size_t index;
	session_info = spdm_context->session_info;
	for (index = 0; index < LIBSPDM_MAX_SESSION_COUNT; index++) {
	if ((session_info[index].session_id & 0xFFFF) == (INVALID_SESSION_ID & 0xFFFF)) {
	rsp_session_id = (uint16_t)(0xFFFF - index);
	return rsp_session_id;
	}
	}
	LIBSPDM_DEBUG((LIBSPDM_DEBUG_ERROR, "libspdm_allocate_rsp_session_id - MAX session_id\n"));
	return (INVALID_SESSION_ID & 0xFFFF);
	}