Increase default datasize limit from 512M to 768M on amd64. This

allows to build xenocara with extra options in malloc.conf.
OK deraadt@

src/etc/etc.amd64/login.conf

@@ -1,4 +1,4 @@
-# $OpenBSD: login.conf,v 1.7 2016/06/26 20:32:31 tedu Exp $
+# $OpenBSD: login.conf,v 1.8 2016/11/25 21:51:29 bluhm Exp $
 
 #
 # Sample login.conf file.  See login.conf(5) for details.
@@ -41,8 +41,8 @@ auth-ftp-defaults:auth-ftp=passwd:
 default:\
 	:path=/usr/bin /bin /usr/sbin /sbin /usr/X11R6/bin /usr/local/bin /usr/local/sbin:\
 	:umask=022:\
-	:datasize-max=512M:\
-	:datasize-cur=512M:\
+	:datasize-max=768M:\
+	:datasize-cur=768M:\
 	:maxproc-max=256:\
 	:maxproc-cur=128:\
 	:openfiles-cur=512:\