David Ahern says:
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Packets that exceed the egress MTU can not be forwarded in the fast path.
Add IPv4 and IPv6 MTU helpers that take a FIB lookup result (versus the
typical dst path) and add the calls to bpf_ipv{4,6}_fib_lookup.
v2
- add ip6_mtu_from_fib6 to ipv6_stub
- only call the new MTU helpers for fib lookups in XDP path; skb
path uses is_skb_forwardable to determine if the packet can be
sent via the egress device from the FIB lookup
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Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>