fou: Remove XRFM from NET_FOU Kconfig

XRFM is no longer needed for configuring FOU tunnels
(CONFIG_NET_FOU_IP_TUNNELS), remove from Kconfig.

Also remove the xrfm.h dependency in fou.c. It was
added in '23461551c006 ("fou: Support for foo-over-udp RX path")'
for depencies of udp_del_offload and udp_offloads, which were removed in
'd92283e338f6 ("fou: change to use UDP socket GRO")'.

Built and installed kernel and setup GUE/FOU tunnels.

Signed-off-by: Coco Li <lixiaoyan@google.com>
Link: https://lore.kernel.org/r/20220411213717.3688789-1-lixiaoyan@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/Kconfig

@@ -321,7 +321,6 @@ config NET_UDP_TUNNEL
 
 config NET_FOU
 	tristate "IP: Foo (IP protocols) over UDP"
-	select XFRM
 	select NET_UDP_TUNNEL
 	help
 	  Foo over UDP allows any IP protocol to be directly encapsulated

net/ipv4/fou.c

@@ -16,7 +16,6 @@
 #include <net/protocol.h>
 #include <net/udp.h>
 #include <net/udp_tunnel.h>
-#include <net/xfrm.h>
 #include <uapi/linux/fou.h>
 #include <uapi/linux/genetlink.h>