hidl_version: add operator!=

This was missing and was needed for a CL internally.

Test: libhidl_test
Change-Id: Ib2cadbfc69b42b6c1ead8a8658adfa40d3ce2a3b
diff --git a/test_main.cpp b/test_main.cpp
index 0de46ec..7f80d71 100644
--- a/test_main.cpp
+++ b/test_main.cpp
@@ -390,12 +390,15 @@
     hidl_version v3_0b{3,0};
 
     EXPECT_TRUE(v1_0 < v2_0);
+    EXPECT_TRUE(v1_0 != v2_0);
     EXPECT_TRUE(v2_0 < v2_1);
     EXPECT_TRUE(v2_1 < v3_0);
     EXPECT_TRUE(v2_0 > v1_0);
+    EXPECT_TRUE(v2_0 != v1_0);
     EXPECT_TRUE(v2_1 > v2_0);
     EXPECT_TRUE(v3_0 > v2_1);
     EXPECT_TRUE(v3_0 == v3_0b);
+    EXPECT_FALSE(v3_0 != v3_0b);
     EXPECT_TRUE(v3_0 <= v3_0b);
     EXPECT_TRUE(v2_2 <= v3_0);
     EXPECT_TRUE(v3_0 >= v3_0b);