test: Set peertimeout in write_config

This avoids having to remember to set it whenever mocktime is used with
peer connections. Also, it might help avoiding disconnects when
attaching a debugger to a running test.

test/functional/test_framework/util.py

@@ -364,6 +364,11 @@ def write_config(config_path, *, n, chain, extra_config="", disable_autoconnect=
         f.write("dnsseed=0\n")
         f.write("fixedseeds=0\n")
         f.write("listenonion=0\n")
+        # Increase peertimeout to avoid disconnects while using mocktime.
+        # peertimeout is measured in wall clock time, so setting it to the
+        # duration of the longest test is sufficient. It can be overriden in
+        # tests.
+        f.write("peertimeout=999999\n")
         f.write("printtoconsole=0\n")
         f.write("upnp=0\n")
         f.write("natpmp=0\n")