RDMA/nes: Use print_mac() to format ethernet addresses for printing

Removing open-coded MAC formats shrinks the source and the generated
code too, eg on x86-64:

add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-103 (-103)
function                                     old     new   delta
make_cm_node                                 932     912     -20
nes_netdev_set_mac_address                   427     406     -21
nes_netdev_set_multicast_list               1148    1124     -24
nes_probe                                   2349    2311     -38

Acked-by: Glenn Streiff <gstreiff@neteffect.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>