If pinfo->desegment_len is non zero, that means that the last
segment in the frame needs to be dissected in a later packet.
On the first pass, we create a MSP.
On later passes, we can retrieve that MSP and use it to look
for its reassembled fragment in order to put the appropriate
reassembled in frame item in the tree.

This increases the cases where reassembled in is inserted in the
tree by including cases where the TLS record has some data
dissected in this frame and some segmented into a later frame.

See analogous TCP commit ec12d0c5