update sources to Ubuntu-4.15.0-39.42

(generated with debian/scripts/import-upstream-tag)

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

diff --git a/submodules/ubuntu-bionic b/submodules/ubuntu-bionic
index 5de3e103785ff53c7c4c317928e758f737b74850..cd8f1d8398a0797776a86138b7e121d5bc435d7a 160000 (submodule)
--- a/submodules/ubuntu-bionic
+++ b/submodules/ubuntu-bionic
@@ -1 +1 @@
-Subproject commit 5de3e103785ff53c7c4c317928e758f737b74850
+Subproject commit cd8f1d8398a0797776a86138b7e121d5bc435d7a