Fix cppcheck warnings

This patch fixes the following cppcheck issues:

git/src/argument.cpp:52:35:
  Parameter 'argv' can be const. [constParameter]

git/src/ncsi_util.hpp:104,105,158,159:
  Missing 'override' on virtuals. [missingOverride]

git/src/ncsi_util.cpp:387:33:
  C-style cast used. [cstyleCast]

git/src/ncsi_util.cpp:654:26:
  'respPayload' not assigned. [unassignedVariable]

static_gateway.cpp:17:60:
  Param 'addr' should be const ref. [passedByValue]

Change-Id: Icb96e9fb891512924febef48b09aaf291a50add1
Signed-off-by: Rashid MP <rashidmp@ami.com>
diff --git a/src/argument.cpp b/src/argument.cpp
index 127780c..f55bb37 100644
--- a/src/argument.cpp
+++ b/src/argument.cpp
@@ -49,7 +49,7 @@
     }
 }
 
-void ArgumentParser::usage(char** argv)
+void ArgumentParser::usage(char* const* argv)
 {
     std::cerr << "Usage: " << argv[0] << " [options]\n";
     std::cerr