sim,python: Flip logic on loopback listeners

People are bitten by allowing external connections to gem5 runs too often
(it happend to me again today). This change flips the logic so the
default is to only allow localhost connections.

Change-Id: If9233f5ca383721017b30b5837a26c5042d925fd
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36175
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Ayaz Akram <yazakram@ucdavis.edu>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/main.py

@@ -97,9 +97,9 @@ def parse_options():
         choices=listener_modes, default="auto",
         help="Port (e.g., gdb) listener mode (auto: Enable if running " \
         "interactively) [Default: %default]")
-    option("--listener-loopback-only", action="store_true", default=False,
-        help="Port listeners will only accept connections over the " \
-        "loopback device")
+    option("--allow-remote-connections", action="store_true", default=False,
+        help="Port listeners will accept connections from anywhere (0.0.0.0). "
+        "Default is only localhost.")
     option('-i', "--interactive", action="store_true", default=False,
         help="Invoke the interactive interpreter after running the script")
     option("--pdb", action="store_true", default=False,
@@ -379,7 +379,7 @@ def main(*args):
     else:
         panic("Unhandled listener mode: %s" % options.listener_mode)
 
-    if options.listener_loopback_only:
+    if not options.allow_remote_connections:
         m5.listenersLoopbackOnly()
 
     # set debugging options