Add back p2p_constants.h to a couple of files

This is a temporary unbreak until we can fix downstream IWYU issues.

Bug: None
No-Try: true
Change-Id: If5f1a600917b22c4c5cfabed050883cafe1c4445
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/383020
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#44230}

p2p/base/port.h

diff --git a/p2p/base/port.h b/p2p/base/port.h
index e0e9171..b029665 100644
--- a/p2p/base/port.h
+++ b/p2p/base/port.h
@@ -33,6 +33,7 @@
 #include "api/transport/stun.h"
 #include "p2p/base/candidate_pair_interface.h"
 #include "p2p/base/connection.h"
+#include "p2p/base/p2p_constants.h"  // IWYU pragma: keep
 #include "p2p/base/port_interface.h"
 #include "p2p/base/transport_description.h"
 #include "rtc_base/async_packet_socket.h"

p2p/base/transport_description.h

diff --git a/p2p/base/transport_description.h b/p2p/base/transport_description.h
index 60a4925..fdc44a2 100644
--- a/p2p/base/transport_description.h
+++ b/p2p/base/transport_description.h
@@ -20,6 +20,7 @@
 #include "absl/algorithm/container.h"
 #include "absl/strings/string_view.h"
 #include "api/rtc_error.h"
+#include "p2p/base/p2p_constants.h"  // IWYU pragma: keep
 #include "rtc_base/ssl_fingerprint.h"
 #include "rtc_base/system/rtc_export.h"