ppp: mppe: Add softdep to arc4

BugLink: https://bugs.launchpad.net/bugs/1838467

[ Upstream commit aad1dcc4 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/ppp/ppp_mppe.c

@@ -62,6 +62,7 @@ MODULE_AUTHOR("Frank Cusack <fcusack@fcusack.com>");
 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