bgpd: Call the doppelganger the doppelganger

bgpd: Call the doppelganger the doppelganger

Currently the code in bgp_accept is calling the
doppelganger `peer`.  This is confusing with
peer and peer1.  Let's just call it doppelganger.

Author's Note:  I am changing the bgp_accept function
in this manner because I find it incredibly confusing
remembering what is what direction and all my other
attempts at getting this straight has caused real
problems.  So I am resorting to doing really small
transformational changes at a time.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>