[mock_tests] Add Sflow Orch UTs (sonic-net#2295)

- What I did
Added Sflow gtest

- Why I did it
Improve sflow orcagent coverage

- How I verified it
ayurkiv@487e531606e9:/sonic/src/sonic-swss/tests/mock_tests$ ./tests --gtest_filter=SflowOrchTest*
Running main() from /build/googletest-YnT0O3/googletest-1.10.0.20201025/googletest/src/gtest_main.cc
Note: Google Test filter = SflowOrchTest*
[==========] Running 2 tests from 1 test suite.
[----------] Global test environment set-up.
[----------] 2 tests from SflowOrchTest
[ RUN      ] SflowOrchTest.SflowEnableDisable
[       OK ] SflowOrchTest.SflowEnableDisable (46 ms)
[ RUN      ] SflowOrchTest.SflowCreateDelete
[       OK ] SflowOrchTest.SflowCreateDelete (46 ms)
[----------] 2 tests from SflowOrchTest (92 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 1 test suite ran. (93 ms total)
[  PASSED  ] 2 tests.

Signed-off-by: Andriy Yurkiv <ayurkiv@nvidia.com>

tests/mock_tests/Makefile.am

@@ -31,6 +31,7 @@ tests_SOURCES = aclorch_ut.cpp \
                 copporch_ut.cpp \
                 saispy_ut.cpp \
                 consumer_ut.cpp \
+                sfloworh_ut.cpp \
                 ut_saihelper.cpp \
                 mock_orchagent_main.cpp \
                 mock_dbconnector.cpp \

tests/mock_tests/mock_orchagent_main.h

@@ -82,3 +82,4 @@ extern sai_queue_api_t *sai_queue_api;
 extern sai_udf_api_t* sai_udf_api;
 extern sai_mpls_api_t* sai_mpls_api;
 extern sai_counter_api_t* sai_counter_api;
+extern sai_samplepacket_api_t *sai_samplepacket_api;

tests/mock_tests/portal.h

@@ -6,6 +6,7 @@
 #include "aclorch.h"
 #include "crmorch.h"
 #include "copporch.h"
+#include "sfloworch.h"
 #include "directory.h"
 
 #undef protected
@@ -82,6 +83,24 @@ struct Portal
         }
     };
 
+    struct SflowOrchInternal
+    {
+        static bool getSflowStatusEnable(SflowOrch &obj)
+        {
+            return obj.m_sflowStatus;
+        }
+
+        static SflowRateSampleMap getSflowSampleMap(SflowOrch &obj)
+        {
+            return obj.m_sflowRateSampleMap;
+        }
+
+        static SflowPortInfoMap getSflowPortInfoMap(SflowOrch &obj)
+        {
+            return obj.m_sflowPortInfoMap;
+        }
+    };
+
     struct DirectoryInternal
     {
         template <typename T>