Fix: multiple consumer locking problems

First, a lot of rcu_read_unlock() were missing the consumer command
handler which could make a rcu lock and return on error without
unlocking.

Fix goto error path in the consumer.

Fix a missing lock control socket mutex.

Fix memory leaks in a UST session where the consumers output object were
not freed during a destroy command.

Add a relayd sockets sent flag so we don't resend existing sockets to
the consumer during an enable_consumer command.

Signed-off-by: David Goulet <dgoulet@efficios.com>