packaging: Use patch for applying patches

`tools/packaging/scripts/apply_patches.sh` uses `git apply $patch`, but
this will not apply to subdirectories. If one wanted to apply with
`git apply`, they'd have to run it with `--directory=...`
_relative to the Git tree's root_ (absolute will not work!). I suggest
we just use `patch`, which will do what we expected `git apply` would
do.

`patch` is also added to build containers that require it.

Fixes: #3690
Signed-off-by: Jakob Naucke <jakob.naucke@ibm.com>

tools/packaging/static-build/kernel/Dockerfile

@@ -16,6 +16,7 @@ RUN apt-get update && \
 	    flex \
 	    git \
 	    iptables \
-	    libelf-dev && \
+	    libelf-dev \
+	    patch && \
     if [ "$(uname -m)" = "s390x" ]; then apt-get install -y --no-install-recommends libssl-dev; fi && \
     apt-get clean && rm -rf /var/lib/lists/