Update bitflags requirement from 1.2 to 2.1 in /lib/vibrio

Updates the requirements on [bitflags](https://github.com/bitflags/bitflags) to permit the latest version.
- [Release notes](https://github.com/bitflags/bitflags/releases)
- [Changelog](https://github.com/bitflags/bitflags/blob/main/CHANGELOG.md)
- [Commits](bitflags/bitflags@1.2.0...2.1.0)

---
updated-dependencies:
- dependency-name: bitflags
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

lib/vibrio/Cargo.toml

@@ -14,7 +14,7 @@ crate-type = ["staticlib", "rlib"]
 [dependencies]
 kpi = { path = "../kpi" }
 lineup = { path = "../lineup" }
-bitflags = "1.2"
+bitflags = "2.1"
 log = "0.4"
 x86 = { version = "0.52", features = ["unstable"] }
 slabmalloc = "0.10"