Put in Ethernet and LLC headers ourselves while sending BPDUs

Put in Ethernet and LLC headers ourselves while sending BPDUs

   Take BPDU contents from RSTPLIB but create the Ethernet and LLC
   headers ourselves. The packet send interface has been modified to
   take an iovec array so we can pass the headers and data to it without
   making copies into another flat buffer.
   RSTPLIB then doesn't even need to know the port MAC addresses if we
   add an interface to configure the bridge address.

Signed-off-by: Srinivas Aji <Aji_Srinivas@emc.com>