Rename DTS_NET_MIRROR to DTS_INT_MIRROR

DTS_INT_MIRROR better contrasts DTS_EXT_MIRROR.

Signed-off-by: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
[iustin@google.com: updated patch for changed context]
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>