Prevent deadlock between PCEP session mgmt and stats thread

Prevent deadlock between PCEP session mgmt and stats thread

Deadlock happens between 2 threads trying to acquire lock on
Stateful07TopologySessionListener and TopologyStatsProviderImpl
instance in reverse order. In AbstractTopologySessionListener#getDelegatedLspsCount(),
locking was added to avoid ConcurrentModificationException for
lspData map. Patch achieves same result without having to acquire
the lock by using thread-safe ConcurrentHashMap for lspData.

JIRA: BGPCEP-901
Change-Id: I74b5070c2e1c8075f5df9504d6eef4de541597fd
Signed-off-by: Ajay Lele <ajayslele@gmail.com>
Signed-off-by: Deepthi V V <dvv@luminanetworks.com>
(cherry picked from commit b481a55c539be1987b303cbfab9fb190b56828dc)