feat: nfsd support as module package

Build nfsd support as module package. This allows to build an nfsd
extension to be used with projects like openebs/dynamic-nfs-provisioner.

Talos can load it via machine-config:
```yaml
machine:
    # Configures the kernel.
    kernel:
        # Kernel modules to load.
        modules:
            - name: nfsd # Module name.
```

Signed-off-by: Subhash Chandra <[email protected]>

Makefile

@@ -72,6 +72,7 @@ TARGETS += \
 	kernel \
 	drbd-pkg \
 	gasket-driver-pkg \
+	nfsd-pkg \
 	nvidia-open-gpu-kernel-modules-pkg \
 
 # Temporarily disabled until mellanox builds with Linux 6.1

nfsd/nfsd.config

@@ -0,0 +1,9 @@
+CONFIG_NFSD=m
+CONFIG_NFSD_V2_ACL=y
+CONFIG_NFSD_V3_ACL=y
+CONFIG_NFSD_V4=y
+# CONFIG_NFSD_BLOCKLAYOUT is not set
+# CONFIG_NFSD_SCSILAYOUT is not set
+# CONFIG_NFSD_FLEXFILELAYOUT is not set
+# CONFIG_NFSD_V4_2_INTER_SSC is not set
+# CONFIG_NFSD_V4_SECURITY_LABEL is not set

nfsd/pkg.yaml

@@ -0,0 +1,28 @@
+name: nfsd-pkg
+variant: scratch
+shell: /toolchain/bin/bash
+dependencies:
+  - stage: kernel-build
+steps:
+  - env:
+      ARCH: '{{ if eq .ARCH "aarch64"}}arm64{{ else if eq .ARCH "x86_64" }}x86_64{{ else }}unsupported{{ end }}'
+    prepare:
+      - |
+        cd /src
+        cat /pkg/nfsd.config >> .config
+    build:
+      - |
+        cd /src
+        make olddefconfig
+        make scripts
+    install:
+      - |
+        cd /src
+        make -j $(nproc) -C /src M=fs/nfsd modules_install DESTDIR=/rootfs INSTALL_MOD_PATH=/rootfs INSTALL_MOD_STRIP=1 CONFIG_MODULE_SIG_ALL=y
+    test:
+      - |
+        # https://www.kernel.org/doc/html/v4.15/admin-guide/module-signing.html#signed-modules-and-stripping
+        find /rootfs/lib/modules -name '*.ko' -exec grep -FL '~Module signature appended~' {} \+
+finalize:
+  - from: /rootfs
+    to: /