Previously, the check to turn on promiscuous mode only took into account
the total number of SHared Receive Address (SHRA) registers and if the
request was for a register within that range.  It is possible that the
Management Engine might have locked a number of SHRA and not allowed a
new address to be written to the requested register.

Add a function to determine the number of unlocked SHRA registers.  Then
determine if the number of registers available is sufficient for our needs,
if not then return -ENOMEM so that UNICAST PROMISC mode is activated.

Since the method by which ME claims SHRA registers is non-deterministic,
also add a return value to the function attempting to write an address
to a SHRA, and return a -E1000_ERR_CONFIG if the write fails.  The error
will be passed up the function chain and allow the driver to also set
UNICAST PROMISC when this happens.

Cc: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Dave Ertman <davidx.m.ertman@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>