streamchain

The state transfer module receives blocks from either the orderer
or other peers, and puts them into a payload buffer for reordering so
they would enter the ledger in-order.

In some cases:
- If the peer joined late and it receives blocks from peers starting from
  index i where the ledger is missing indices [j, i] for some j<i
  and the rate of block reception from peers is very fast
- If the ledger is "stuck" (i.e file system full, etc.) and cannot advance

This buffer would overpopulate.

This commit addresses this, and adds a maximum distance constant
that if the difference between the ledger height and the sequence
of the block that is received is greater than this constant,
the block is dropped.

Change-Id: Ia1ba8966ea6d211c5d1b7ddd84a4fad34af797d4
Signed-off-by: yacovm <yacovm@il.ibm.com>