Fix L2 flood packet replication interaction with VXLAN-tunnel

The check for input sw_if_index against output sw_if_index is not correct
for the interface on the replication order after VXLAN tunnel because the
encap code overwrite packet sw_if_index[VLIB_RX] with that of the VXLAN
tunnel sw_if_index. The check should be done using sw_if_index[VLIB_RX]
saved in the packet context.

Change-Id: I175717221409977e80576e84dfe5362d1f6aed2f
Signed-off-by: John Lo <loj@cisco.com>