net/netip: optimize Addr.MarshalText allocation for 4in6 addresses

net/netip: optimize Addr.MarshalText allocation for 4in6 addresses

name                           old time/op    new time/op    delta
AddrMarshalText/v4-8             18.5ns ± 1%    18.8ns ± 1%   +1.40%  (p=0.000 n=9+10)
AddrMarshalText/v6-8             58.0ns ± 0%    57.5ns ± 0%   -0.93%  (p=0.000 n=9+10)
AddrMarshalText/v6_ellipsis-8    61.4ns ± 0%    60.4ns ± 0%   -1.65%  (p=0.000 n=10+9)
AddrMarshalText/v6_v4-8          25.7ns ± 0%    26.2ns ± 1%   +1.86%  (p=0.000 n=10+10)
AddrMarshalText/v6_zone-8        61.8ns ± 0%    60.8ns ± 0%   -1.63%  (p=0.000 n=10+9)

name                           old alloc/op   new alloc/op   delta
AddrMarshalText/v4-8              16.0B ± 0%     16.0B ± 0%     ~     (all equal)
AddrMarshalText/v6-8              48.0B ± 0%     48.0B ± 0%     ~     (all equal)
AddrMarshalText/v6_ellipsis-8     48.0B ± 0%     48.0B ± 0%     ~     (all equal)
AddrMarshalText/v6_v4-8           48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=10+10)
AddrMarshalText/v6_zone-8         48.0B ± 0%     48.0B ± 0%     ~     (all equal)

name                           old allocs/op  new allocs/op  delta
AddrMarshalText/v4-8               1.00 ± 0%      1.00 ± 0%     ~     (all equal)
AddrMarshalText/v6-8               1.00 ± 0%      1.00 ± 0%     ~     (all equal)
AddrMarshalText/v6_ellipsis-8      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
AddrMarshalText/v6_v4-8            1.00 ± 0%      1.00 ± 0%     ~     (all equal)
AddrMarshalText/v6_zone-8          1.00 ± 0%      1.00 ± 0%     ~     (all equal)

Change-Id: Ib298a0fb9ec6b55e37d0559dad387242dc82aab9
Reviewed-on: https://go-review.googlesource.com/c/go/+/557776
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>