flowcache: Bring net/core/flow.c under IPsec maintain scope

As flow cache is mainly manipulated from IPsec.

Signed-off-by: Fan Du <fan.du@windriver.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

MAINTAINERS

diff --git a/MAINTAINERS b/MAINTAINERS
index 091b50e..f6bc618 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5992,6 +5992,7 @@
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec.git
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next.git
 S:	Maintained
+F:	net/core/flow.c
 F:	net/xfrm/
 F:	net/key/
 F:	net/ipv4/xfrm*