The kernel modules for rtl8319 are missing in boot2docker which
prevents booting it from kvm which appears to use rtl8319 as the network interface by default on debian 10 (buster) started via docker-machine with the kvm driver (which does not set the interface type).

With following config (copied from my ubuntu 20.04 config, so I am not sure all are needed) boot2docker gets correct network interfaces when started with kvm:

--- a/files/kernel-config.d/boot2docker
+++ b/files/kernel-config.d/boot2docker
@@ -7,4 +7,8 @@ CONFIG_IKCONFIG=m
 CONFIG_IKCONFIG_PROC=y
 CONFIG_KERNEL_XZ=y
 CONFIG_KSM=y
+CONFIG_8139CP=m
+CONFIG_8139TOO=m
+CONFIG_8139TOO_PIO=y
+CONFIG_8139TOO_8129=y
 CONFIG_LOCALVERSION="-boot2docker"