s3:rpc_server: Switch to core dcerpc server loop

s3:rpc_server: Switch to core dcerpc server loop

This commit finally switches the RPC server implementation.

At the same we have to do other related changes to keep code compiling
and test environments running.

First avoid moving the session_info into the allocated pipes_struct memory
context as it is owned now by the core RPC server, and the s3compat pidl
compiler will update the pipes_struct session_info before dispatching
the call with dcesrv_call->auth_state->session_info.

Also, fix a segfault in the endpoint mapper daemon when it tries to delete
the endpoints previously registered over a NCALRPC connection.

If we have:

rpc_server : epmapper = external
rpc_server : lsarpc = external
rpc_daemon : epmd = fork
rpc_daemon : lsasd = fork

The sequence is:

* The endpoint mapper starts (start_epmd in source3/smbd/server.c)
* The lsarpc daemon starts (start_lsasd in source3/smbd/server.c)
  * The lsarpc daemon creates the sockets and registers its endpoints
    (rpc_ep_register in source3/rpc_server/lsasd.c)
  * The endpoint registration code opens a NCALRPC connection to the
    endpoint mapper daemon (ep_register in source3/librpc/rpc/dcerpc_ep.c)
    and keeps it open to re-register if the endpoint mapper daemon dies
    (rpc_ep_register_loop in source3/rpc_server/rpc_ep_register.c)
* When the endpoint mapper daemon accepts a NCALRPC connection it sets a
  termination function (srv_epmapper_delete_endpoints)
* Suppose the lsarpc daemon exits. The NCALRPC connection termination
  function is called.
* The termination function tries to delete all endpoints registered by that
  connection by calling _epm_Delete
* _epm_Delete calls is_privileged_pipe which access to
  pipes_struct->session_info.

As the call to _epm_Delete occurs outside of the PIDL generated code,
the pipes_stuct->session_info is NULL. This commit also sets
pipes_struct->session_info from the dcerpc_connection before calling
_epm_Delete. As the core rpc server supports security context multiplexing we
need to pass the dcesrv_connection to the termination function and let the
implementation pick a auth context. In the case of the endpoint mapper
the termination function has to pick one of type NCALRPC_AS_SYSTEM to
check if the connection is privileged and delete the endpoints
registered by the connection being closed.

Finally, the samba.tests.dcerpc.raw_protocol testsuite passes against
the ad_member environment.

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>