[Ada] Fix IPv6 numeric address detection

IPv6 numeric address can't have less than 2 colons. It fixes the error
when Get_Host_By_Name called with hostname composed by only hexadecimal
symbols.

2019-08-12  Dmitriy Anisimkov  <anisimko@adacore.com>

gcc/ada/

	* libgnat/g-socket.adb (Is_IPv6_Address): Check that no less
	then 2 colons in IPv6 numeric address.

From-SVN: r274308

gcc/ada/ChangeLog

 2019-08-12  Dmitriy Anisimkov  <anisimko@adacore.com>
 
+	* libgnat/g-socket.adb (Is_IPv6_Address): Check that no less
+	then 2 colons in IPv6 numeric address.
+
+2019-08-12  Dmitriy Anisimkov  <anisimko@adacore.com>
+
 	* libgnat/g-comlin.ads, libgnat/g-comlin.adb (Getopt): Add
 	parameter Quiet. Need to do not output error messages to
 	console. Invalid_Switch exception generation surrounded by an

gcc/ada/libgnat/g-socket.adb

@@ -1797,7 +1797,7 @@ package body GNAT.Sockets is
          end if;
       end loop;
 
-      return Colons <= 8;
+      return Colons in 2 .. 8;
    end Is_IPv6_Address;
 
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