msgr: clear_pipe inside pipe_lock on mark_down_all

Observed a segfault in rebind -> mark_down_all -> clear_pipe -> put that
may have been due to a racing thread clearing the connection_state pointer.
Do the clear_pipe() call under the protection of pipe_lock, as we do in
all other contexts.

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: clear con->pipe inside pipe_lock on mark_down

We need to do this under protection of the pipe_lock.

Signed-off-by: Sage Weil <sage@inktank.com>
msg/Pipe: goto fail_unlocked on early failures in accept()

Instead of duplicating an incomplete cleanup sequence (that does not
clear_pipe()), goto fail_unlocked and do the cleanup in a generic way.
s/rc/r/ while we are here.

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: reaper: make sure pipe has been cleared (under pipe_lock)

All paths to pipe shutdown should have cleared the con->pipe reference
already.  Assert as much.

Also, do it under pipe_lock!

Signed-off-by: Sage Weil <sage@inktank.com>
msgr: clear_pipe+queue reset when replacing lossy connections

We already handle the lossless replacement and lossy fault paths, but
not the lossy replacement.  This fixes an assert(!cleared) in the
reaper.  Adjust comments appropriately.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #375 from ceph/wip-msgr

misc msgr fixes

Reviewed-by: Greg Farnum <greg@inktank.com>