mds: use 128 bits for waiters on MDSCacheObject

mds: use 128 bits for waiters on MDSCacheObject

Adding a new inode lock will overflow inode wait bits into the MDSCacheObject
wait bits. Make space for the quiescelock.

This includes a minor refactor to no longer attempt scoping the set of masks we
test in MDSCacheObject::waiting when calling MDSCacheObject::is_waiter_for.
This optimization wasn't worth the overhead and would be awkard to keep as
std::bitset cannot be used as a key for a std::multimap (easily).  Instead, we
use the sequence number as a key which helps us to avoid allocating another map
whenever we call MDSCacheObject::take_waiting.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>