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>

include/net/9p/9p.h

@@ -595,4 +595,5 @@ int p9_idpool_check(int id, struct p9_idpool *p);
 
 int p9_error_init(void);
 int p9_errstr2errno(char *, int);
+int p9_trans_fd_init(void);
 #endif /* NET_9P_H */

include/net/9p/transport.h

@@ -96,5 +96,4 @@ struct p9_trans_module {
 void v9fs_register_trans(struct p9_trans_module *m);
 struct p9_trans_module *v9fs_match_trans(const substring_t *name);
 struct p9_trans_module *v9fs_default_trans(void);
-
 #endif /* NET_9P_TRANSPORT_H */