Previously, all incoming messages would be blocked before a DL_CONF
message arrives from the TCP/IP stack. This however makes it impossible
for a driver to process interrupts before the DL_CONF initialization.
This patch blocks only datalink messages before the initial DL_CONF,
and lets through all other messages to the driver.
Change-Id: I89988958c0bff9bb38e0379b66f6142491a67b61