Keepalive value of 0 in BaseConnection class causes issues for long-running tasks with intermediary firewalls

[awilki01]

While waiting for an SCP file transfer to complete (over an hour), I will get a 'Socket is closed' exception. When I manually set the keepalive to 30, the problem no longer occurs. I'm requesting a default value of 30 be placed in the library.

[ktbyers]

Keepalive of non-zero would reduce risk of firewalls or network devices themselves from purging the connection.