Peter Wu authored Nov 17, 2018 and AndersBroman committed Nov 20, 2018

Support reading and writing pcapng files with DSBs. A DSB may occur
multiple times but should appear before packets that need those
decryption secrets (so it cannot be moved to the end like NRB). The TLS
dissector will be updated in the future to make use of these secrets.
pcapng spec update: https://github.com/pcapng/pcapng/pull/54

As DSBs may be interleaved with packets, do not even try to read it in
pcapng_open (as is done for IDBs). Instead process them during the
sequential read, appending them to the 'wtap::dsbs' array.

Writing is more complicated, secrets may initially not be available when
'wtap_dumper' is created. As they may become available in 'wtap::dsbs'
as more packets are read, allow 'wtap_dumper::dsbs_growing' to reference
this array. This saves every user from checking/dumping DSBs.

If the wtap user needs to insert extra DSBs (while preserving existing
DSBs), they can set the 'wtap_dumper::dsbs_initial' field.

The test...