9p: fix bad kconfig cross-dependency

This patch moves transport dynamic registration and matching to the net
module to prevent a bad Kconfig dependency between the net and fs 9p modules.

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

diff --git a/net/9p/mux.c b/net/9p/mux.c
index 934e2ea..f140147 100644
--- a/net/9p/mux.c
+++ b/net/9p/mux.c
@@ -31,6 +31,7 @@
 #include <linux/idr.h>
 #include <linux/mutex.h>
 #include <net/9p/9p.h>
+#include <linux/parser.h>
 #include <net/9p/transport.h>
 #include <net/9p/conn.h>