shill: Fix most of warnings from cpplint

Fix most cpplinter's warnings. On a few occasisions, the warnings
produced were false-positives, so added explicit // NOLINT comment
overrides.

There were a few instances of disallowed non-const reference usage
(reported as runtime/reference error by cpplint) for
"DBus::Error &error" which should potentially be changed
to pointers to comply with C++ coding style but I will let Shill
owners do that since there is quite a few of those and the
change isn't brain-dead simple...

BUG=None
TEST=platform2 still compiles and all unit tests pass.

Change-Id: Ic2e31896aa13d20eeb1a85dee74f3db8cccfde2e
Reviewed-on: https://chromium-review.googlesource.com/204164
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/mm1_modem_proxy.cc b/mm1_modem_proxy.cc
index 017781d..3e4563f 100644
--- a/mm1_modem_proxy.cc
+++ b/mm1_modem_proxy.cc
@@ -18,7 +18,7 @@
 template<typename TraceMsgT, typename CallT, typename CallbackT,
          typename... ArgTypes>
 void ModemProxy::BeginCall(
-    const TraceMsgT &trace_msg, const CallT &call, CallbackT &callback,
+    const TraceMsgT &trace_msg, const CallT &call, const CallbackT &callback,
     Error *error, int timeout, ArgTypes... rest) {
   BeginAsyncDBusCall(trace_msg, proxy_, call, callback, error,
                      &CellularError::FromMM1DBusError, timeout, rest...);