When the function dev_get_phys_port_name was added it missed a description
for it's len argument. Adding it.
Fixes: 3b4b7751dbbd ("net: add support for phys_port_name") Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com> Signed-off-by: David S. Miller <davem@davemloft.net>