ecryptfs: discard ecryptfsd registration messages in miscdev

The userspace eCryptfs daemon sends HELO and QUIT messages to the kernel
for per-user daemon (un)registration.  These messages are required when
netlink is used as the transport, but (un)registration is handled by
opening and closing the device file when miscdev is the transport.  These
messages should be discarded in the miscdev transport so that a daemon
isn't registered twice.

Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>