Restoring a huge table is a synchronous operation

[shamis]

While restoring a big table the session is getting blocked. No other action can be performed on dderl while the restoring is going on.

[acautin]

@shamis after reviewing the code I found it is not serialized in dderl side as it is as any other normal request so it is probably getting stuck in the imem side so no other operation is getting a response until this one finishes.

Moving this to imem.