Fix jenkins.sh failure for kernels >= 6.3.0

In >= 6.3.0 the default for how modules are built in absence of
vmlinux.o or Module.symvers due to a change of the modpost execution.

See linux kernel git commit 5573b4daa26a0cf15aa0fecd7f1be16e0b6157bc

As our build verification *just* builds the dahdi modules without
building the entire kernel, we need to enforce the legacy behaviour
by adding KBUILD_MODPOST_WARN=1 to the command line.

Change-Id: I7206f1daed8ff1e7fcd4894bc24e5ef4d4590358
---
M contrib/jenkins.sh
1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index eeb3fbc..6a39daf 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -29,4 +29,4 @@
 git log -1 --pretty="%t - %s"
 
 make -j "$JOBS" modules_prepare
-make -j "$JOBS" -C "$TOPDIR" KSRC="$KSRC"
+make -j "$JOBS" -C "$TOPDIR" KSRC="$KSRC" KBUILD_MODPOST_WARN=1

