refactor: zfs version patch logic is more correct (#14)

this merge changes nothing about new builds as they already don't patch, but makes logic more correct for anyone trying to build an older zfs version into a custom image.

build-kmod-zfs.sh

@@ -28,13 +28,21 @@ curl -L -O https://github.com/openzfs/zfs/releases/download/zfs-${ZFS_VERSION}/z
 tar xzf zfs-${ZFS_VERSION}.tar.gz
 
 # patch the zfs-kmod.spec.in file for older zfs versions
+ZFS_MAJ=$(echo $ZFS_VERSION | cut -f1 -d.)
 ZFS_MIN=$(echo $ZFS_VERSION | cut -f2 -d.)
 ZFS_PATCH=$(echo $ZFS_VERSION | cut -f3 -d.)
-if [ "${ZFS_MIN}" -lt "3" ]; then
-    if [ "${ZFS_PATCH}" -lt "3" ]; then
-        patch  -b -uN -i zfs-kmod-spec-in.patch zfs-${ZFS_VERSION}/rpm/generic/zfs-kmod.spec.in
-    fi
+DO_PATCH=1
+if [ "${ZFS_MAJ}" -lt "2" ]; then
+    DO_PATCH=0
+elif [ "${ZFS_MAJ}" -eq "2" ] && [ "${ZFS_MIN}" -lt "2" ]; then
+    DO_PATCH=0
+elif [ "${ZFS_MAJ}" -eq "2" ] && [ "${ZFS_MIN}" -eq "2" ] && [ "${ZFS_PATCH}" -lt "3" ]; then
+    DO_PATCH=0
 fi
+if [ "${DO_PATCH}" -eq "0" ]; then
+    patch  -b -uN -i zfs-kmod-spec-in.patch zfs-${ZFS_VERSION}/rpm/generic/zfs-kmod.spec.in
+fi
+
 cd /tmp/zfs-${ZFS_VERSION}
 ./configure \
         -with-linux=/usr/src/kernels/${KERNEL}/ \