ipaddr: remove unnecessary allocation in Aggregate
ipaddr: remove unnecessary allocation in Aggregate

name             old time/op    new time/op    delta
AggregateIPv4    30.6µs ± 8%    30.9µs ± 9%     ~     (p=0.139 n=50+50)
AggregateIPv6    10.3µs ± 4%    10.0µs ± 5%   -3.49%  (p=0.000 n=50+50)

name             old alloc/op   new alloc/op   delta
AggregateIPv4    3.12kB ± 0%    2.98kB ± 0%   -4.62%  (p=0.000 n=50+50)
AggregateIPv6    2.61kB ± 0%    1.78kB ± 0%  -31.90%  (p=0.000 n=50+50)

name             old allocs/op  new allocs/op  delta
AggregateIPv4      58.0 ± 0%      56.0 ± 0%   -3.45%  (p=0.000 n=50+50)
AggregateIPv6      34.0 ± 0%      32.0 ± 0%   -5.88%  (p=0.000 n=50+50)

mikioh/ipaddr