MAINTAINERS: add missing IPv4/IPv6 header paths

Add missing headers to the IP entry.
Reviewed-by: NDavid Ahern <dsahern@kernel.org>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -13461,7 +13461,11 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git
 F:	arch/x86/net/*
+F:	include/linux/ip.h
+F:	include/linux/ipv6*
+F:	include/net/fib*
 F:	include/net/ip*
+F:	include/net/route.h
 F:	net/ipv4/
 F:	net/ipv6/