vma: State that vma->fd is -1 constant in the image

This field was lost while switching to protobuf -- the vma images
were used by parasite as plain array and it was easier to reseve
this space in the image. Now it's too late to change this, so make
it be -1 always.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -166,6 +166,13 @@ static int read_and_open_vmas(int pid, struct list_head *vmas, int *nr_vmas)
 		if (ret <= 0)
 			break;
 
+		if (e->fd != -1) {
+			ret = -1;
+			pr_err("Error in vma->fd setting (%Ld)\n", 
+					(unsigned long long)e->fd);
+			break;
+		}
+
 		vma->vma = *e;
 		vma_entry__free_unpacked(e, NULL);
 

protobuf/vma.proto

@@ -6,5 +6,8 @@ message vma_entry {
 	required uint32		prot	= 5;
 	required uint32		flags	= 6;
 	required uint32		status	= 7;
+	// This fd thing is unused in the image, it was lost
+	// while switching from execve restore model. It is
+	// -1 by default.
 	required sint64		fd	= 8;
 }