Expose the SOA query transport type used before/during XFR
This is the second part of the series implementing a feature requested by #3883 (closed) (parts one and three being !7984 (merged) and !8305 (merged)).
Add a new field in the incoming zone transfers section of the statistics channel to show the transport used for the SOA request.
When the transfer is started beginning from the XFRST_SOAQUERY state, it means that the SOA query will be performed by xfrin itself, using the same transport. Otherwise, it means that the SOA query was already performed by other means (e.g. by zone.c:soa_query()), and, in that case, we use the SOA query transport type information passed by the 'soa_transport_type' argument, when the xfrin object was created.
Edited by Arаm Sаrgsyаn