[L2TP]: Add the ability to autoload a pppox protocol module.

This patch allows a name "pppox-proto-nnn" to be used in modprobe.conf
to autoload a PPPoX protocol nnn.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/pppox.c

diff --git a/drivers/net/pppox.c b/drivers/net/pppox.c
index 3f8115d..f3e47d0 100644
--- a/drivers/net/pppox.c
+++ b/drivers/net/pppox.c
@@ -31,6 +31,7 @@
 #include <linux/ppp_defs.h>
 #include <linux/if_ppp.h>
 #include <linux/ppp_channel.h>
+#include <linux/kmod.h>
 
 #include <net/sock.h>
 
@@ -114,6 +115,13 @@
 		goto out;
 
 	rc = -EPROTONOSUPPORT;
+#ifdef CONFIG_KMOD
+	if (!pppox_protos[protocol]) {
+		char buffer[32];
+		sprintf(buffer, "pppox-proto-%d", protocol);
+		request_module(buffer);
+	}
+#endif
 	if (!pppox_protos[protocol] ||
 	    !try_module_get(pppox_protos[protocol]->owner))
 		goto out;