Report template flush events via JSON

[cameronkerrnz]

Occassionally, when looking at the debug output, you see:

[ipfix_col] drop template 0:279
[ipfix_col] drop template 0:278
[ipfix_col] drop template 0:277
[ipfix_col] drop template 0:276
[ipfix_col] drop template 0:275
[ipfix_col] drop template 0:274
[ipfix_col] drop template 0:273
[ipfix_col] drop template 0:272
[ipfix_col] drop template 0:271
[ipfix_col] drop template 0:270
[ipfix_col] drop template 0:269
[ipfix_col] drop template 0:267
[ipfix_col] drop template 0:266
[ipfix_col] drop template 0:265
[ipfix_col] drop template 0:264
[ipfix_col] drop template 0:263
[ipfix_col] drop template 0:262
[ipfix_col] drop template 0:261
[ipfix_col] drop template 0:260
[ipfix_col] drop template 0:259
[ipfix_col] drop template 0:258
[ipfix_col] drop template 0:257
[ipfix_col] drop template 0:256

Like #22, it would be useful to have some sort of status-lock on the templates: pre-loading or cache-locking at least would be useful.