system_api: add comments for port numbers

Clarify that kGarconPort is what garcon connects to, not listens on.
No functional change.

BUG=b:231500896
TEST=CQ

Change-Id: I31f2a3e13ddcd0809efa0e6613701abff815bf87
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/3708621
Reviewed-by: Fergus Dall <sidereal@google.com>
Tested-by: Emil Mikulic <easy@google.com>
Commit-Queue: Emil Mikulic <easy@google.com>
Auto-Submit: Emil Mikulic <easy@google.com>
NOKEYCHECK=True
GitOrigin-RevId: a69c4fc8d337500a10a21e7fe4b3d1826e58bd39
diff --git a/constants/vm_tools.h b/constants/vm_tools.h
index e6fa2b9..574c10a 100644
--- a/constants/vm_tools.h
+++ b/constants/vm_tools.h
@@ -8,7 +8,11 @@
 namespace vm_tools {
 
 constexpr int kMaitredPort = 8888;
+
+// Static port number that vm_cicerone (running in the host) listens on, and
+// garcon (in the container) connects to.
 constexpr int kGarconPort = 8889;
+
 constexpr int kTremplinPort = 8890;
 constexpr int kVshPort = 9001;
 constexpr int kArcHostClockServicePort = 9901;
@@ -16,6 +20,8 @@
 constexpr int kDefaultStartupListenerPort = 7777;
 constexpr int kTremplinListenerPort = 7778;
 constexpr int kCrashListenerPort = 7779;
+
+// Static port number that ARCVM runs sftp-server on.
 constexpr int kSftpServerPort = 7780;
 
 constexpr int kLmkdKillDecisionPort = 7781;