tg3: Update link_up flag for phylib devices

Commit f4a46d1f introduced a bug where
the ifconfig stats would remain 0 for phylib devices. This is due to
tp->link_up flag never becoming true causing tg3_periodic_fetch_stats()
to return.

The link_up flag was being updated in tg3_test_and_report_link_chg()
after setting up the phy. This function however, is not called for
phylib devices since the driver does not do the phy setup.

This patch moves the link_up flag update into the common
tg3_link_report() function that gets called for phylib devices as well
for non phylib devices when the link state changes.

To avoid updating link_up twice, we replace tg3_carrier_...() calls that
are followed by tg3_link_report(), with netif_carrier_...(). We can then
remove the unused tg3_carrier_on() function.

CC: <stable@vger.kernel.org>
Reported-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>