bmv2: move p4 path to a BMV2Net parameter

Allow users to specify custom paths to p4.
Co-authored-by: Antoine Kaufmann <antoinek@mpi-sws.org>

experiments/simbricks/orchestration/simulators.py

@@ -915,6 +915,7 @@ class BMV2Net(NetSim):
     def __init__(self):
         super().__init__()
         self.sync = False
+        self.p4_path = 'sims/net/p4/basic.json'
 
     def run_cmd(self, env):
         cmd = (
@@ -932,7 +933,11 @@ class BMV2Net(NetSim):
         for _, n in self.connect_sockets(env):
             cmd += f' -i {port}@{n}'
             port += 1
-        cmd += ' ' + env.repodir + '/sims/net/p4/basic.json'
+
+        if self.p4_path.startswith('/'):
+            cmd += f' {self.p4_path}'
+        else:
+            cmd += f' {env.repodir}/{self.p4_path}'
 
         print(cmd)