Updated the Rock2 to Kernel 4.6-rc1:

.........
Fedora 23 (Twenty Three)
Kernel 4.6.0-rc1 on an armv7l (ttyS2)
....................
# uname -a
Linux rgrock2 4.6.0-rc1 #1 SMP Sun Mar 27 03:47:06 EDT 2016 armv7l armv7l armv7l GNU/Linux

The stmmac Ethernet driver bug from 4.5 Final has still not been fixed, and the driver code has changed in 4.6-rc1, and copying the 4.5-rc7 drivers no longer worked..
So.. I created patches from the diff between the 4.5-rc7 and 4.5 Final versions, and applied them to the 4.6-rc1 source..
~/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
and
~/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c

[root@rgrock2 src]# cat stmmac_mdio_fix.patch |patch -p0
patching file a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
[root@rgrock2 src]# cat stmmac_platform_fix.patch |patch -p0
patching file b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
Hunk #1 succeeded at 146 (offset 36 lines).
Hunk #2 succeeded at 176 (offset 36 lines).

The re-compiled, and re-booted, and Ethernet appears to work OK:

rk_gmac-dwmac ff290000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

But.. further tests show the link does not work..

$ sftp rgrock2
ssh: connect to host rgrock2 port 22: No route to host
Couldn't read packet: Connection reset by peer
.....
$ ping rgrock2
PING rgrock2 (192.168.0.xx) 56(84) bytes of data.
From rglinux-i7 (192.168.0.xxx) icmp_seq=1 Destination Host Unreachable
From rglinux-i7 (192.168.0.xxx) icmp_seq=2 Destination Host Unreachable
From rglinux-i7 (192.168.0.xxx) icmp_seq=3 Destination Host Unreachable

Robert Gadsdon.   March 27, 2016. – Updated..