prov/efa: Make DGRAM provider use new av_entry struct

Update the DGRAM provider to use the new efa_base_av_entry structure.
This change splits the AV logic for the DGRAM and the RDM providers.
Splitting the av logic for DGRAM makes DGRAM's AV logic simpler and
faster in a few ways.

1. This change removes the efa_con struct from the av_entry because the
   DGRAM protocol does not maintain an idea of a connection to the
   endpoint receiving the messages. It does not matter if the remote
   endpoint we were previously communicating with exits, and a new QP
   opens with the same AH (NIC), and QPN (Endpoint). As long as someone
   is there to post recv buffers for our messages, DGRAM provider is
   happy.

2. This changes gets rid of the current/prev av reverse lookup map
   (ahn/qpn -> av_entry), and creates a single reverse look up map
   because the dgram provider does not care about old connections.

Signed-off-by: Seth Zegelstein <[email protected]>