Add type cast to fix build error with "-Wsign-compare" cflag.

There is build error if "-Wsign-compare" is defined in cflags.
Also add "-Wsign-compare" to Android.bp

Test: Build

Change-Id: If41da96ec521a0d2dcddf660e7effa218c99810d
Signed-off-by: Sehee Park <sehee32.park@samsung.com>
diff --git a/server/XfrmControllerTest.cpp b/server/XfrmControllerTest.cpp
index 5f74e32..1613905 100644
--- a/server/XfrmControllerTest.cpp
+++ b/server/XfrmControllerTest.cpp
@@ -300,18 +300,18 @@
     EXPECT_EQ(DROID_SPI, static_cast<int>(userspi.max));
 }
 
-void verifyXfrmiArguments(int mark, int mask, int ifId) {
+void verifyXfrmiArguments(uint32_t mark, uint32_t mask, uint32_t ifId) {
     // Check that correct arguments (and only those) are non-zero, and correct.
-    EXPECT_EQ(0, mark);
-    EXPECT_EQ(0, mask);
+    EXPECT_EQ(0U, mark);
+    EXPECT_EQ(0U, mask);
     EXPECT_EQ(TEST_XFRM_IF_ID, ifId);
 }
 
-void verifyVtiArguments(int mark, int mask, int ifId) {
+void verifyVtiArguments(uint32_t mark, uint32_t mask, uint32_t ifId) {
     // Check that correct arguments (and only those) are non-zero, and correct.
     EXPECT_EQ(TEST_XFRM_MARK, mark);
     EXPECT_EQ(TEST_XFRM_MASK, mask);
-    EXPECT_EQ(0, ifId);
+    EXPECT_EQ(0U, ifId);
 }
 
 void testIpSecAddSecurityAssociation(testCaseParams params, const MockSyscalls& mockSyscalls,
@@ -446,10 +446,10 @@
         EXPECT_TRUE(fwmark.explicitlySelected);
         EXPECT_TRUE(fwmark.protectedFromVpn);
     } else {
-        EXPECT_EQ(0, outputmark.outputMark);
-        EXPECT_EQ(0, mark.mark.v);
-        EXPECT_EQ(0, mark.mark.m);
-        EXPECT_EQ(0, xfrm_if_id.if_id);
+        EXPECT_EQ(0U, outputmark.outputMark);
+        EXPECT_EQ(0U, mark.mark.v);
+        EXPECT_EQ(0U, mark.mark.m);
+        EXPECT_EQ(0U, xfrm_if_id.if_id);
     }
 }