net: core,vrf: Change pcpu_dstat fields to u64_stats_t

The pcpu_sw_netstats and pcpu_lstats structs both contain a set of
u64_stats_t fields for individual stats, but pcpu_dstats uses u64s
instead.

Make this consistent by using u64_stats_t across all stats types.

The per-cpu dstats are only used by the vrf driver at present, so update
that driver as part of this change.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240607-dstats-v3-1-cc781fe116f7@codeconstruct.com.au


Signed-off-by: Jakub Kicinski <kuba@kernel.org>