[Comb] Move utilities to common libraries, Pull logic for buffer conf…

…iguration into helper function, Migrate some users to ReadStreamChannelResponsesAndFinish, Toggle port speed before test, Adding packet, Add tolerance for Queue stats check, Renamed Packet to PacketAtPort, L3 admit tests should choose only ports that are UP & Update L3 Admit Test to not rely on a custom GNMI Config.

tests/forwarding/BUILD.bazel

@@ -205,7 +205,6 @@ cc_library(
     srcs = ["l3_admit_test.cc"],
     hdrs = ["l3_admit_test.h"],
     deps = [
-	":mirror_blackbox_test_fixture",
         ":util",
         "//gutil:proto",
         "//gutil:status_matchers",
@@ -215,16 +214,17 @@ cc_library(
         "//p4_pdpi:p4_runtime_session",
         "//p4_pdpi/packetlib",
         "//p4_pdpi/packetlib:packetlib_cc_proto",
-        "//sai_p4/instantiations/google:instantiations",
-        "//sai_p4/instantiations/google:sai_p4info_cc",
         "//tests/lib:p4info_helper",
 	"//tests/lib:p4rt_fixed_table_programming_helper",
         "//tests/lib:packet_in_helper",
+        "//tests/lib:switch_test_setup_helpers",
         "//thinkit:mirror_testbed_fixture",
+        "//thinkit:switch",
         "@com_github_google_glog//:glog",
         "@com_github_p4lang_p4runtime//:p4info_cc_proto",
         "@com_github_p4lang_p4runtime//:p4runtime_cc_proto",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:statusor",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/strings:str_format",
         "@com_google_absl//absl/time",
@@ -348,3 +348,11 @@ cc_library(
         "@com_google_googletest//:gtest",
     ],
 )
+
+cc_library(
+    name = "packet_at_port",
+    hdrs = [
+        "packet_at_port.h",
+    ],
+    deps = ["@com_google_absl//absl/strings"],
+)