ipv6-range: Only calculate number of /56s when appropriate

Commit e61762e ("ipv6-range: Display number of /56's where appropriate"
started displaying the number of /56 networks a given network provides,
however this broke when given a prefixlen of > 56, e.g

  ./ipv6-range 2001:db8:abc:cc00::/60
  Network : 2001:db8:abc:cc00::/60 (268435456 /56 networks, 16 /64 networks)
  Start   : 2001:0db8:0abc:cc00:0000:0000:0000:0000
  End     : 2001:0db8:0abc:cccf:ffff:ffff:ffff:ffff

So only display the number of /56s when the prefixlen is < 56, e.g

  ./ipv6-range 2001:db8:abc:cc00::/60
  Network : 2001:db8:abc:cc00::/60 (16 /64 networks)
  Start   : 2001:0db8:0abc:cc00:0000:0000:0000:0000
  End     : 2001:0db8:0abc:cc0f:ffff:ffff:ffff:ffff

  ./ipv6-range 2001:db8:abc::/48
  Network : 2001:db8:abc::/48 (256 /56 networks, 65536 /64 networks)
  Start   : 2001:0db8:0abc:0000:0000:0000:0000:0000
  End     : 2001:0db8:0abc:ffff:ffff:ffff:ffff:ffff

Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000

ipv6-range.c

@@ -43,13 +43,19 @@ static void ipv6_range(const char *network, unsigned short prefixlen)
 	}
 
 	/*
-	 * For a prefix length of < 64, calculate the number of /64 networks
-	 * the given network provides. E.g a /48 provides 65536 /64's
+	 * For a prefix length of < 56, calculate the number of /56 and
+	 * /64 networks the given network provides. E.g a /48 provides
+	 * 256 /56 and 65536 /64 networks.
+	 *
+	 * For a prefix length of < 64, just display the nubmer of /64s.
 	 */
-	if (prefixlen < 64)
+	if (prefixlen < 56)
 		snprintf(net_s, sizeof(net_s), "(%u /56 networks, "
 				"%zu /64 networks)", 1 << (56 - prefixlen),
 				(networks >> prefixlen) + 1);
+	else if (prefixlen < 64)
+		snprintf(net_s, sizeof(net_s), "(%zu /64 networks)",
+				(networks >> prefixlen) + 1);
 
 	printf("Network : %s/%u %s\n", network, prefixlen, net_s);
 	printf("Start   : ");