net, internal/poll: reset value before adding in minor kernel version

Fixes #42733

Change-Id: I5446aeb5de13cd70212755fb12c9bc484f343c74
Reviewed-on: https://go-review.googlesource.com/c/go/+/271846
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/internal/poll/copy_file_range_linux.go

@@ -35,6 +35,7 @@ func kernelVersion() (major int, minor int) {
 			if vi >= len(values) {
 				break
 			}
+			value = 0
 		}
 	}
 	switch vi {

src/net/sock_linux.go

@@ -27,6 +27,7 @@ func kernelVersion() (major int, minor int) {
 			if vi >= len(values) {
 				break
 			}
+			value = 0
 		}
 	}
 	switch vi {