Re-order the fields of 'struct h2_session_props' to avoid a hole and some padding.

Re-order the fields of 'struct h2_session_props' to avoid a hole and some padding.

On x86_64, this shrinks the size of the struct from 40 to 32 bytes.

Before the patch, pahole states that:

struct h2_session_props {
	int                        accepted_max;         /*     0     4 */
	int                        completed_max;        /*     4     4 */
	int                        emitted_count;        /*     8     4 */
	int                        emitted_max;          /*    12     4 */
	int                        error;                /*    16     4 */

	/* XXX 4 bytes hole, try to pack */

	const char  *              error_msg;            /*    24     8 */
	unsigned int               accepting:1;          /*    32: 0  4 */
	unsigned int               shutdown:1;           /*    32: 1  4 */

	/* size: 40, cachelines: 1, members: 8 */
	/* sum members: 28, holes: 1, sum holes: 4 */
	/* sum bitfield members: 2 bits (0 bytes) */
	/* padding: 4 */
	/* bit_padding: 30 bits */
	/* last cacheline: 40 bytes */
};

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1907756 13f79535-47bb-0310-9956-ffa450edef68