stubdom: explcitly add libc and lwip Mini-OS config options

Today the Mini-OS build systems derives libc and lwip config options
from the stubdom and LWIPDIR make variables supplied by the Xen build
system.

In order to prepare those being explicit Mini-OS config options, add
them to the related stubdom Mini-OS config files.

While at it remove the CONFIG_START_NETWORK setting from config files
disabling lwip, as CONFIG_START_NETWORK requires lwip for becoming
effective.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

stubdom/xenstore-minios.cfg

@@ -1,3 +1,4 @@
+CONFIG_LIBC=y
 CONFIG_BLKFRONT=n
 CONFIG_NETFRONT=n
 CONFIG_FBFRONT=n