Fix a couple of panics when detaching from a cxgbe/cxl interface that was

never brought up:
- Allow NULL to be passed to sglist_free().
- Don't try to stop an interface that was never fully initialized.

Reviewed by:	np

sys/dev/cxgbe/t4_main.c

@@ -3292,6 +3292,12 @@ cxgbe_uninit_synchronized(struct port_info *pi)
 
 	ASSERT_SYNCHRONIZED_OP(sc);
 
+	if (!(pi->flags & PORT_INIT_DONE)) {
+		KASSERT(!(ifp->if_drv_flags & IFF_DRV_RUNNING),
+		    ("uninited port is running"));
+		return (0);
+	}
+
 	/*
 	 * Disable the VI so that all its data in either direction is discarded
 	 * by the MPS.  Leave everything else (the queues, interrupts, and 1Hz

sys/kern/subr_sglist.c

@@ -216,6 +216,9 @@ void
 sglist_free(struct sglist *sg)
 {
 
+	if (sg == NULL)
+		return;
+
 	if (refcount_release(&sg->sg_refs))
 		free(sg, M_SGLIST);
 }