Implement INetd.aidl getProcSysNet().

Also: a few "tidy-inspired" changes.

Test: as follows
    - built, flashed, booted
    - system/netd/tests/runtest.sh passes
Bug: 32163131
Change-Id: Icaa164af3c3d0d03af1ec083dfcbe856ac51529f
diff --git a/server/NetdNativeService.h b/server/NetdNativeService.h
index b34e363..c8b85f0 100644
--- a/server/NetdNativeService.h
+++ b/server/NetdNativeService.h
@@ -93,9 +93,10 @@
     binder::Status interfaceDelAddress(const std::string &ifName,
             const std::string &addrString, int prefixLength) override;
 
-    binder::Status setProcSysNet(
-            int32_t family, int32_t which, const std::string &ifname, const std::string &parameter,
-            const std::string &value) override;
+    binder::Status getProcSysNet(int32_t ipversion, int32_t which, const std::string& ifname,
+                                 const std::string& parameter, std::string* value) override;
+    binder::Status setProcSysNet(int32_t ipversion, int32_t which, const std::string& ifname,
+                                 const std::string& parameter, const std::string& value) override;
 
     // Metrics reporting level set / get (internal use only).
     binder::Status getMetricsReportingLevel(int *reportingLevel) override;