ibmvnic: Add set_link_state routine for setting adapter link state

Create a common routine for setting the link state for the vnic adapter.
This update moves the sending of the crq and waiting for the link state
response to a common place. The new routine also adds handling of
resending the crq in cases of getting a partial success response.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>