[TG3]: Fix supporting flowctrl code

This patch does three things.  It modifies tg3_setup_flow_control() to
use the administrator requested flow control settings if
autonegotiation is turned off.  It slightly modifies the
tg3_setup_fiber_mii_phy() function to account for this new use case.
And finally, it does the same for tg3_setup_copper_phy().

The copper modifications are more than a small multi-line change.  The
new code makes an attempt to avoid a link renegotiation if the link is
active at half duplex and the only difference between the current
advertised settings and requested advertised settings is the
flow control advertisements.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>