9p: fix error path during early mount

There was some cleanup issues during early mount which would trigger
a kernel bug for certain types of failure.  This patch reorganizes the
cleanup to get rid of the bad behavior.

This also merges the 9pnet and 9pnet_fd modules for the purpose of
configuration and initialization.  Keeping the fd transport separate
from the core 9pnet code seemed like a good idea at the time, but in
practice has caused more harm and confusion than good.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

net/9p/Kconfig

@@ -13,16 +13,6 @@ menuconfig NET_9P
 
 	  If unsure, say N.
 
-config NET_9P_FD
-	depends on NET_9P
-	default y if NET_9P
-	tristate "9P File Descriptor Transports (Experimental)"
-	help
-	  This builds support for file descriptor transports for 9p
-	  which includes support for TCP/IP, named pipes, or passed
-	  file descriptors.  TCP/IP is the default transport for 9p,
-	  so if you are going to use 9p, you'll likely want this.
-
 config NET_9P_VIRTIO
 	depends on NET_9P && EXPERIMENTAL && VIRTIO
 	tristate "9P Virtio Transport (Experimental)"