cxgb4: Rename t4_link_start() to t4_link_l1cfg

t4_link_start() was completely misnamed.  It does _not_ start up the
link. It merely does the L1 Configuration for the link. The Link Up
process is started automatically by the firmware when the number of
enabled Virtual Interfaces on a port goes from 0 to 1. So renaming
this routine to t4_link_l1cfg() for better documentation.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>