ppp: Fix PPPIOCUNBRIDGECHAN request number

PPPIOCGL2TPSTATS already uses 54. This shouldn't be a problem in
practice, but let's keep the logical decreasing assignment scheme.

Fixes: 4cf476ce ("ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Link: https://lore.kernel.org/r/e3a4c355e3820331d8e1fffef8522739aae58b57.1608380117.git.gnault@redhat.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/uapi/linux/ppp-ioctl.h

@@ -116,7 +116,7 @@ struct pppol2tp_ioc_stats {
 #define PPPIOCGCHAN	_IOR('t', 55, int)	/* get ppp channel number */
 #define PPPIOCGL2TPSTATS _IOR('t', 54, struct pppol2tp_ioc_stats)
 #define PPPIOCBRIDGECHAN _IOW('t', 53, int)	/* bridge one channel to another */
-#define PPPIOCUNBRIDGECHAN _IO('t', 54)	/* unbridge channel */
+#define PPPIOCUNBRIDGECHAN _IO('t', 52)	/* unbridge channel */
 
 #define SIOCGPPPSTATS   (SIOCDEVPRIVATE + 0)
 #define SIOCGPPPVER     (SIOCDEVPRIVATE + 1)	/* NEVER change this!! */