MAINTAINERS: exclude 9p from networking

We don't have much to say about 9p, even tho it lives under net/.
Avoid CCing netdev.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -15068,6 +15068,7 @@ F:	lib/random32.c
 F:	net/
 F:	tools/net/
 F:	tools/testing/selftests/net/
+X:	net/9p/
 X:	net/bluetooth/
 
 NETWORKING [IPSEC]