Disable some PortAllocatorTest on valgrind memcheck due to flakiness

BUG=webrtc:4743
R=kjellander@webrtc.org

Review URL: https://codereview.webrtc.org/1146923006

Cr-Commit-Position: refs/heads/master@{#9382}
diff --git a/tools/valgrind-webrtc/gtest_exclude/rtc_unittests.gtest-memcheck.txt b/tools/valgrind-webrtc/gtest_exclude/rtc_unittests.gtest-memcheck.txt
index 86895e5..3130e1d 100644
--- a/tools/valgrind-webrtc/gtest_exclude/rtc_unittests.gtest-memcheck.txt
+++ b/tools/valgrind-webrtc/gtest_exclude/rtc_unittests.gtest-memcheck.txt
@@ -10,4 +10,6 @@
 # Issue 3447
 P2PTransportChannelMultihomedTest.TestFailover
 P2PTransportChannelMultihomedTest.TestDrain
-
+# Issue 4743
+PortAllocatorTest.TestDisableAllPorts
+PortAllocatorTest.TestGetAllPortsNoUdpSockets