Fix some errors related to snooping and functional access in the bus

Fix some errors related to snooping and functional access in the bus

src/mem/bus.cc:
    Only call snoop once per port, need to fix it so snoop ranges that overlap aren't added to list
    Functional accesses that call snoop and it goes to a higher bus may change the src, reset it after each snoop.

--HG--
extra : convert_revision : 7276059c798a85cb9d138ccc5531298ecd055c13