s3:rpc_server: Unify RPC client disconnect and termination functions

s3:rpc_server: Unify RPC client disconnect and termination functions

These functions are used by endpoint mapper to delete the endpoints
when a NCALRPC connection from an external daemon is lost and by
preforked childs to accept the next client as soon as the current
connection terminates. We can use the same function for both purposes.

Signed-off-by: Samuel Cabrero <scabrero@suse.de>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>