Wait in the acceptor if we get emfile errors

This should avoid using all CPU because we keep trying to accept.

src/ranch_acceptor.erl

@@ -39,6 +39,11 @@ loop(LSocket, Transport, ConnsSup) ->
 			%% This call will not return until process has been started
 			%% AND we are below the maximum number of connections.
 			ranch_conns_sup:start_protocol(ConnsSup, CSocket);
+		%% Reduce the accept rate if we run out of file descriptors.
+		%% We can't accept anymore anyway, so we might as well wait
+		%% a little for the situation to resolve itself.
+		{error, emfile} ->
+			receive after 100 -> ok end;
 		%% We want to crash if the listening socket got closed.
 		{error, Reason} when Reason =/= closed ->
 			ok