ppp: mppe: Add softdep to arc4

The arc4 crypto is mandatory at ppp_mppe probe time, so let's put a
softdep line, so that the corresponding module gets prepared
gracefully.  Without this, a simple inclusion to initrd via dracut
failed due to the missing dependency, for example.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
index ff61dd8..66c8e65 100644
--- a/drivers/net/ppp/ppp_mppe.c
+++ b/drivers/net/ppp/ppp_mppe.c
@@ -63,6 +63,7 @@
 MODULE_DESCRIPTION("Point-to-Point Protocol Microsoft Point-to-Point Encryption support");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("ppp-compress-" __stringify(CI_MPPE));
+MODULE_SOFTDEP("pre: arc4");
 MODULE_VERSION("1.0.2");
 
 static unsigned int