l2: fix null deref in l2_to_bvi()

Type: fix

Static analysis identified a possible null pointer dereference. It
was introduced by a recent patch which expanded the DMAC comparison
on inbound packets on a BVI interface to include any secondary MAC
addresses which were added to an interface.

Check if the pointer is null before dereferencing.

Change-Id: Ic2afe2b062eda32977e05bf3f98d82c1fe64620c
Signed-off-by: Matthew Smith <mgsmith@netgate.com>

Author: mgsmith1000

src/vnet/l2/l2_bvi.h

@@ -72,7 +72,7 @@ l2_to_bvi (vlib_main_t * vlib_main,
       ethernet_interface_t *ei = ethernet_get_interface (em, hi->hw_if_index);
       u32 rv;
 
-      if (PREDICT_FALSE (vec_len (ei->secondary_addrs) > 0))
+      if (PREDICT_FALSE (ei && (vec_len (ei->secondary_addrs) > 0)))
 	rv = l2_to_bvi_dmac_check (hi, e0->dst_address, ei,
 				   1 /* have_sec_dmac */ );
       else