License header and pass object state clearing

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

dsp_ff-plugin/dsp_ff.cc

diff --git a/dsp_ff-plugin/dsp_ff.cc b/dsp_ff-plugin/dsp_ff.cc
index 11555f8..1a2c0a9 100644
--- a/dsp_ff-plugin/dsp_ff.cc
+++ b/dsp_ff-plugin/dsp_ff.cc
@@ -682,6 +682,12 @@
             log_cmd_error("No rules file specified!");
         }
 
+        // Reset state
+        m_CellsToRemove.clear();
+        m_DspChanges.clear();
+        m_DspTypes.clear();
+        m_FlopTypes.clear();
+
         // Load rules
         rewrite_filename(rulesFile);
         load_rules(rulesFile);

dsp_ff-plugin/nexus-dsp_rules.txt

diff --git a/dsp_ff-plugin/nexus-dsp_rules.txt b/dsp_ff-plugin/nexus-dsp_rules.txt
index fa11c3f..934eea5 100644
--- a/dsp_ff-plugin/nexus-dsp_rules.txt
+++ b/dsp_ff-plugin/nexus-dsp_rules.txt
@@ -1,3 +1,11 @@
+# Copyright (C) 2020-2022  The SymbiFlow Authors.
+#
+# Use of this source code is governed by a ISC-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/ISC
+#
+# SPDX-License-Identifier:ISC
+
 dsp MULT9X9 MULT18X18 MULT18X36 MULT36X36
   port A
     clk CLK 0