net: cache IPv6 zone information for applications using IPv6 link-local address
This change reduces the overhead of calling routing information per IPv6
link-local datagram read by caching IPv6 addressing scope zone
information.
Fixes #15237.
name old time/op new time/op delta
UDP6LinkLocalUnicast-8 64.9µs ± 0% 18.6µs ± 0% -71.30%
name old alloc/op new alloc/op delta
UDP6LinkLocalUnicast-8 11.2kB ± 0% 0.2kB ± 0% -98.42%
name old allocs/op new allocs/op delta
UDP6LinkLocalUnicast-8 101 ± 0% 3 ± 0% -97.03%
Change-Id: I5ae2ef5058df1028bbb7f4ab32b13edfb330c3a7
Reviewed-on: https://go-review.googlesource.com/21952 Reviewed-by: Ian Lance Taylor <iant@golang.org>