ixgbe: wait for link after copper MAC setup

After setting up the link on x552/X557-AT 10GBASE-T NICs, sometimes the
link does not get set up properly and as a result all the subsequent
calls to ixgbe_check_link() from ixgbe_dev_link_update_share() fail.

Introduce a delay time of 1s in ixgbe_setup_mac_link_t_X550em() before
beginning to set up the external PHY link speed to ensure that the
controller can acquire the link.

Signed-off-by: Ashijeet Acharya <ashijeet.acharya@6wind.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>

Approved by: imp
Obtained from: DPDK (d31b95860d8e9dd7c6e242bd08baaac00a9714f0)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D31621