Lwt_utils.never_ending is a global variable, hence a GC root. A promise
created by binding it cannot ever be garbage collected. This fixes the
known leak in the baker an endorser by allocating a fresh one for each
use (by turning it into a function). This porbably fix other slower
leaks.
High five Klakplok and Vincent.
This allows a node to specify that it doesn't want to receive operations
that are not included in a block. To do so, one should use the new
--disable-mempool option.
A disabled mempool node announce its configuration during the ACK exchange.
This configuration should be easily expandable with other options.
Node will keep track of the ack exchange configuration for each nodes it
is connected to and will not propagate its mempool to disabled mempool
nodes.
A disabled mempool node will ignore non-empty mempool received.
In the future, this incident should be punish by a decrement of its score
and / or ban.
Notes:
1. P2p_socket.Rejected -> P2p_errors.Rejected_socket_connection
to avoid conflict with P2p_pool.Rejected
2. Connection_closed error in P2p_pool unused and redundant with one
in P2p_io_scheduler
