linux/common-config: leave FOU options to defaults

Since IPV6_FOU_TUNNEL was set, I get an unexpected ip6tnl device at
boot.  It was set to y to accomodate Linux 7.1 divergences between
aacrh64 and x86_64, but by just not setting NET_FOU or
IPV6_FOU_TUNNEL, I get everything built as modules on both platforms,
like we presumably want.

Fixes: be994ce8a8 ("linux/common-config: update for 7.1")

pkgs/os-specific/linux/kernel/common-config.nix

@@ -319,14 +319,12 @@ let
       IPV6_MROUTE = yes;
       IPV6_MROUTE_MULTIPLE_TABLES = yes;
       IPV6_PIMSM_V2 = yes;
-      IPV6_FOU_TUNNEL = yes;
       IPV6_SEG6_LWTUNNEL = yes;
       IPV6_SEG6_HMAC = yes;
       IPV6_SEG6_BPF = yes;
       NET_CLS_ACT = yes;
       NET_CLS_BPF = module;
       NET_ACT_BPF = module;
-      NET_FOU = yes;
       NET_SCHED = yes;
       NET_SCH_BPF = whenAtLeast "6.16" (whenPlatformHasEBPFJit yes);
       L2TP_V3 = yes;