FS-11607: [mod_sofia] Fix Windows build regression by adding missing sofia_json_api.c to the build.

src/mod/endpoints/mod_sofia/mod_sofia.2017.vcxproj

@@ -167,6 +167,7 @@
     <ClCompile Include="sip-dig.c" />
     <ClCompile Include="sofia.c" />
     <ClCompile Include="sofia_glue.c" />
+    <ClCompile Include="sofia_json_api.c" />
     <ClCompile Include="sofia_media.c" />
     <ClCompile Include="sofia_presence.c" />
     <ClCompile Include="sofia_reg.c" />