MAINTAINERS: update PPP OVER L2TP file patterns

Commit 21b4aaa1 ("l2tp: Relocate pppol2tp
driver to new net/l2tp directory") moved the file.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: James Chapman <jchapman@katalix.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -4531,7 +4531,7 @@ F:	drivers/net/pppox.c
 PPP OVER L2TP
 M:	James Chapman <jchapman@katalix.com>
 S:	Maintained
-F:	drivers/net/pppol2tp.c
+F:	net/l2tp/l2tp_ppp.c
 F:	include/linux/if_pppol2tp.h
 
 PPS SUPPORT