libnetdriver: only block datalink messages

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
Use ARM_VM_SECTION_MASK to determine kernel base address

To map kernel we use 1M sections therefore we should use
ARM_VM_SECTION_MASK to determine base address.

Change-Id: I0b97fe459f2325d702aad9b7b1e8e066d9721b87
beaglebone ethernet improvements

	. added enable interrupts routine at the HW init stage
	. remove workaround, obsoleted by libnetdriver change
	. change netconf.sh to allow configuring this driver,
	  changed README.txt to reflect this

Change-Id: Ib659d5a55be96022b5e9013caa556dca5092ce89