MAP MASQ: Fix config file reload

As config file reload may be triggered from a process elsewhere, we need
to explicitly specify the Application name 'mgw_nat' to access the
application environment.
diff --git a/src/map_masq.erl b/src/map_masq.erl
index cd840d6..c2e1e1b 100644
--- a/src/map_masq.erl
+++ b/src/map_masq.erl
@@ -420,9 +420,9 @@
 % Configuration file has changed, re-generate internal data structures
 config_update() ->
 	% (re-)generate the MAP Address rewrite table
-	{ok, MapRewriteTbl} = application:get_env(map_rewrite_table),
+	{ok, MapRewriteTbl} = application:get_env(mgw_nat, map_rewrite_table),
 	MapRewriteTblOut = generate_rewrite_table(MapRewriteTbl),
-	application:set_env(map_rewrite_table, MapRewriteTblOut),
+	application:set_env(mgw_nat, map_rewrite_table, MapRewriteTblOut),
 	%{ok, MsrnPfxStp} = application:get_env(msrn_pfx_stp),
 	%{ok, MsrnPfxMsc} = application:get_env(msrn_pfx_msc),
 	%{ok, IntPfx} = application:get_env(intern_pfx),