Revert "build: drop clap from dev-dependencies"

This reverts commit 998fb48ff2.

This is breaking the release build process (cross build for aarch64
musl) so temporarily reverting until we can identify the cause to allow
the release proceeed.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vhost_user_net/Cargo.toml

@@ -18,3 +18,5 @@ virtio-bindings = "0.1.0"
 vm-memory = "0.10.0"
 vmm-sys-util = "0.11.0"
 
+[build-dependencies]
+clap = { version = "4.0.29", features = ["cargo"] }