Fix heartbeat device treatment.

Fix heartbeat device treatment.

wd_create_hb_recv_socket() and wd_create_hb_send_socket() called
setsockopt(2) with wrong argument.

	struct ifreq i;
	strlcpy(i.ifr_name, hb_if->if_name, sizeof(i.ifr_name));
	if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, &i, sizeof(i)) == -1)
	:

This is not quite correct since the 4th argument should be
just a null terminated string (device name), not struct ifreq.

Discussion: [pgpool-hackers: 4602] heartbeat and SO_BINDTODEVICE
https://www.pgpool.net/pipermail/pgpool-hackers/2025-May/004603.html
Backpatch-through: v4.6