Remove dead ifaddr.c fallback code.

We carried a special implementation of pg_foreach_ifaddr() using
Solaris's ioctl(SIOCGLIFCONF), but Solaris 11 and illumos adopted
getifaddrs() more than a decade ago, and we prefer to use that.  Solaris
10 is EOL'd.  Remove the dead code.

Adjust comment about which OSes have getifaddrs(), which also
incorrectly listed AIX.  AIX is in fact the only Unix in the build farm
that *doesn't* have it today, so the implementation based on
ioctl(SIOCGIFCONF) (note, no 'L') is still live.  All the others have
had it for at least one but mostly two decades.

The last-stop fallback at the bottom of the file is dead code in
practice, but it's hard to justify removing it because the better
options are all non-standard.

Discussion: https://postgr.es/m/CA+hUKGKErNfhmvb_H0UprEmp4LPzGN06yR2_0tYikjzB-2ECMw@mail.gmail.com

Author: macdice

src/backend/libpq/ifaddr.c

@@ -302,7 +302,7 @@ pg_foreach_ifaddr(PgIfAddrCallback callback, void *cb_data)
  * for each one.  Returns 0 if successful, -1 if trouble.
  *
  * This version uses the getifaddrs() interface, which is available on
- * BSDs, AIX, and modern Linux.
+ * BSDs, macOS, Solaris, illumos and Linux.
  */
 int
 pg_foreach_ifaddr(PgIfAddrCallback callback, void *cb_data)
@@ -332,115 +332,7 @@ pg_foreach_ifaddr(PgIfAddrCallback callback, void *cb_data)
 #include <sys/sockio.h>
 #endif
 
-/*
- * SIOCGIFCONF does not return IPv6 addresses on Solaris.
- * So we prefer SIOCGLIFCONF if it's available.
- */
-
-#if defined(SIOCGLIFCONF)
-
-/*
- * Enumerate the system's network interface addresses and call the callback
- * for each one.  Returns 0 if successful, -1 if trouble.
- *
- * This version uses ioctl(SIOCGLIFCONF).
- */
-int
-pg_foreach_ifaddr(PgIfAddrCallback callback, void *cb_data)
-{
-	struct lifconf lifc;
-	struct lifreq *lifr,
-				lmask;
-	struct sockaddr *addr,
-			   *mask;
-	char	   *ptr,
-			   *buffer = NULL;
-	size_t		n_buffer = 1024;
-	pgsocket	sock,
-				fd;
-
-#ifdef HAVE_IPV6
-	pgsocket	sock6;
-#endif
-	int			i,
-				total;
-
-	sock = socket(AF_INET, SOCK_DGRAM, 0);
-	if (sock == PGINVALID_SOCKET)
-		return -1;
-
-	while (n_buffer < 1024 * 100)
-	{
-		n_buffer += 1024;
-		ptr = realloc(buffer, n_buffer);
-		if (!ptr)
-		{
-			free(buffer);
-			close(sock);
-			errno = ENOMEM;
-			return -1;
-		}
-
-		memset(&lifc, 0, sizeof(lifc));
-		lifc.lifc_family = AF_UNSPEC;
-		lifc.lifc_buf = buffer = ptr;
-		lifc.lifc_len = n_buffer;
-
-		if (ioctl(sock, SIOCGLIFCONF, &lifc) < 0)
-		{
-			if (errno == EINVAL)
-				continue;
-			free(buffer);
-			close(sock);
-			return -1;
-		}
-
-		/*
-		 * Some Unixes try to return as much data as possible, with no
-		 * indication of whether enough space allocated. Don't believe we have
-		 * it all unless there's lots of slop.
-		 */
-		if (lifc.lifc_len < n_buffer - 1024)
-			break;
-	}
-
-#ifdef HAVE_IPV6
-	/* We'll need an IPv6 socket too for the SIOCGLIFNETMASK ioctls */
-	sock6 = socket(AF_INET6, SOCK_DGRAM, 0);
-	if (sock6 == PGINVALID_SOCKET)
-	{
-		free(buffer);
-		close(sock);
-		return -1;
-	}
-#endif
-
-	total = lifc.lifc_len / sizeof(struct lifreq);
-	lifr = lifc.lifc_req;
-	for (i = 0; i < total; ++i)
-	{
-		addr = (struct sockaddr *) &lifr[i].lifr_addr;
-		memcpy(&lmask, &lifr[i], sizeof(struct lifreq));
-#ifdef HAVE_IPV6
-		fd = (addr->sa_family == AF_INET6) ? sock6 : sock;
-#else
-		fd = sock;
-#endif
-		if (ioctl(fd, SIOCGLIFNETMASK, &lmask) < 0)
-			mask = NULL;
-		else
-			mask = (struct sockaddr *) &lmask.lifr_addr;
-		run_ifaddr_callback(callback, cb_data, addr, mask);
-	}
-
-	free(buffer);
-	close(sock);
-#ifdef HAVE_IPV6
-	close(sock6);
-#endif
-	return 0;
-}
-#elif defined(SIOCGIFCONF)
+#if defined(SIOCGIFCONF)
 
 /*
  * Remaining Unixes use SIOCGIFCONF. Some only return IPv4 information