initramfs-build: Fix buildroot defconfig

The glibc version has moved on; accept the default from buildroot.
We also specifiy that DHCP should run on eth0.

Change-Id: Ic0e899320fca1eebd0493908a669b0d684a79714
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/initramfs-build.sh b/initramfs-build.sh
index 4c56730..4af4ec0 100755
--- a/initramfs-build.sh
+++ b/initramfs-build.sh
@@ -75,7 +75,7 @@
 BR2_TARGET_ROOTFS_CPIO=y
 BR2_TARGET_ROOTFS_CPIO_XZ=y
 BR2_TARGET_GENERIC_GETTY_PORT="hvc0"
-BR2_GLIBC_VERSION_2_22=y
+BR2_SYSTEM_DHCP="eth0"
 EOF_BUILDROOT
 
 # Build buildroot