Solve compiler warning related to string size

"enable" is 6 characters, and doing a strncmp for 7 bytes leads to
compiler warnings about the extra character.

Bug: None
Test: build
Change-Id: I17e3093baeca55cccb46601491cbf497c338d27d
diff --git a/server/NdcDispatcher.cpp b/server/NdcDispatcher.cpp
index 7692a9c..e957db8 100644
--- a/server/NdcDispatcher.cpp
+++ b/server/NdcDispatcher.cpp
@@ -304,7 +304,7 @@
                              false);
                 return 0;
             }
-            int enable = !strncmp(argv[3], "enable", 7);
+            int enable = !strncmp(argv[3], "enable", 6);
             Status status = mNetd->interfaceSetIPv6PrivacyExtensions(std::string(argv[2]), enable);
             if (status.isOk()) {
                 cli->sendMsg(ResponseCode::CommandOkay, "IPv6 privacy extensions changed", false);
@@ -321,7 +321,7 @@
                 return 0;
             }
 
-            int enable = !strncmp(argv[3], "enable", 7);
+            int enable = !strncmp(argv[3], "enable", 6);
             Status status = mNetd->interfaceSetEnableIPv6(std::string(argv[2]), enable);
             if (status.isOk()) {
                 cli->sendMsg(ResponseCode::CommandOkay, "IPv6 state changed", false);