udp: move udpv4_offload and udpv6_offload to net_hotdata

These structures are used in GRO and GSO paths.
Move them to net_hodata for better cache locality.

v2: udpv6_offload definition depends on CONFIG_INET=y

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240306160031.874438-12-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>