add kiss radio env to most of the variants

variants/lilygo_tlora_c6/platformio.ini

@@ -84,3 +84,8 @@ build_src_filter = ${tlora_c6.build_src_filter}
 lib_deps =
   ${tlora_c6.lib_deps}
   densaugeo/base64 @ ~1.4.0
+
+[env:LilyGo_Tlora_C6_kiss_modem]
+extends = tlora_c6
+build_src_filter = ${tlora_c6.build_src_filter}
+  +<../examples/kiss_modem/>