mesh: compact incoming segmented messages in lower + upper transport

mesh: store current segment in mesh-upper-transport-builder

mesh: introduce mesh_upper_transport_builder

mesh: track alloc error in message builder finalize

mesh: introduce finalize function for access and upper transport builders

mesh: extract mesh_upper_transport_message builder from mesh_access_message builder

mesh: extend mesh_upper_transport_pdu_free to handle mesh_upper_transport_pdus

mesh: remove mesh_access_pdu_t getters

mesh: remove mesh_message_pdu_t getters (mesh_message_*)

mesh: replace network_header in mesh_segmented_pdu by individual fields

mesh: replace network_header in mesh_control_pdu_t by individual fields

mesh: replace network_header in mesh_access_pdu_t by individual fields

mesh: remove incoming_access_pdu_encrypted_singleton pdu

mesh: free incoming encrypted access pdu until fully processed

mesh: use union for mesh-access and mesh-control pdu singletons, use mesh-access singleton as crypto buffer

mesh: allocate segments for segmented access pdu in run function

mesh: store lower transport pdu in upper pdu field, remove temp globals

mesh: allocate network pdu for outgoing unsegmented access message in run function

mesh: use upper_transport_outgoing_active list instead of single pointer

mesh: remove mesh_unsegmented_pdu_t

mesh: use mesh_network_pdu for unsegmented control and access messages, sort functions

mesh: use mesh_upper_transport_pdu for outgoing segmented control

mesh: use mesh_network_pdu/unsegmented_control for unsegmented control

mesh: delete previous upper transport code for sending access messages

mesh: use only segments in mesh_upper_transport_pdu_t, use mesh_upper_transport_pdu for unsegmented access