devel/libqsbr: create port

Epoch-Based Reclamation (EBR) and Quiescent-State-Based Reclamation (QSBR) are
synchronisation mechanisms which can be used for efficient memory/object
reclamation (garbage collection) in concurrent environment. Conceptually they
are very similar to the read-copy-update (RCU) mechanism.

WWW: https://github.com/rmind/libqsbr

Will be used by npf port