bgpd: Optimize memory for peer_connection struct

bgpd: Optimize memory for peer_connection struct

```
struct peer_connection {
	struct peer *              peer;                 /*     0     8 */
	enum bgp_fsm_status        status;               /*     8     4 */
	enum bgp_fsm_status        ostatus;              /*    12     4 */
	int                        fd;                   /*    16     4 */
	uint32_t                   thread_flags;         /*    20     4 */
	pthread_mutex_t            io_mtx;               /*    24    40 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	struct stream_fifo *       ibuf;                 /*    64     8 */
	struct stream_fifo *       obuf;                 /*    72     8 */
	struct ringbuf *           ibuf_work;            /*    80     8 */
	struct event *             t_read;               /*    88     8 */
	struct event *             t_write;              /*    96     8 */
	struct event *             t_connect;            /*   104     8 */
	struct event *             t_delayopen;          /*   112     8 */
	struct event *             t_start;              /*   120     8 */
	/* --- cacheline 2 boundary (128 bytes) --- */
	struct event *             t_holdtime;           /*   128     8 */
	struct event *             t_connect_check_r;    /*   136     8 */
	struct event *             t_connect_check_w;    /*   144     8 */
	struct event *             t_gr_restart;         /*   152     8 */
	struct event *             t_gr_stale;           /*   160     8 */
	struct event *             t_generate_updgrp_packets; /*   168     8 */
	struct event *             t_pmax_restart;       /*   176     8 */
	struct event *             t_routeadv;           /*   184     8 */
	/* --- cacheline 3 boundary (192 bytes) --- */
	struct event *             t_process_packet;     /*   192     8 */
	struct event *             t_process_packet_error; /*   200     8 */
	union sockunion            su;                   /*   208   128 */

	/* size: 336, cachelines: 6, members: 25 */
	/* last cacheline: 16 bytes */
};   /* saved 8 bytes! */
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>