Add in new RSTP implementation to replace RSTPLIB.

Add in new RSTP implementation to replace RSTPLIB.

   We have a new implementation of RSTP, which is meant to implement the
   Spanning Tree Protocol in IEEE 802.1D-2004. This implementation is
   written as a library consisting of one .c file and one .h file.
   It is written from scratch directly from the 802.1D-2004 document.
   This commit adds the files rstp.h and rstp.c to the directory, in
   preparation for modifying other code to use this instead of rstplib.

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