ethernet: fix coverity 214973

Ensure that the ethernet_input_inline_dmac_check which directly derefererences ei,
is called only if ei is set.

Type: fix
Change-Id: I2d3bce63ee457825a5d375a6102225f3abf67703
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/src/vnet/ethernet/node.c b/src/vnet/ethernet/node.c
index c1a8e0d..4ef575a 100644
--- a/src/vnet/ethernet/node.c
+++ b/src/vnet/ethernet/node.c
@@ -1563,21 +1563,20 @@
 
 		  dmacs[0] = *(u64 *) e0;
 
-		  if (ei && vec_len (ei->secondary_addrs))
-		    ethernet_input_inline_dmac_check (hi, dmacs,
-						      dmacs_bad,
-						      1 /* n_packets */ ,
-						      ei,
-						      1 /* have_sec_dmac */ );
-		  else
-		    ethernet_input_inline_dmac_check (hi, dmacs,
-						      dmacs_bad,
-						      1 /* n_packets */ ,
-						      ei,
-						      0 /* have_sec_dmac */ );
+		  if (ei)
+		    {
+		      if (vec_len (ei->secondary_addrs))
+			ethernet_input_inline_dmac_check (
+			  hi, dmacs, dmacs_bad, 1 /* n_packets */, ei,
+			  1 /* have_sec_dmac */);
+		      else
+			ethernet_input_inline_dmac_check (
+			  hi, dmacs, dmacs_bad, 1 /* n_packets */, ei,
+			  0 /* have_sec_dmac */);
 
-		  if (dmacs_bad[0])
-		    error0 = ETHERNET_ERROR_L3_MAC_MISMATCH;
+		      if (dmacs_bad[0])
+			error0 = ETHERNET_ERROR_L3_MAC_MISMATCH;
+		    }
 
 		skip_dmac_check0:
 		  vlib_buffer_advance (b0, sizeof (ethernet_header_t));