e1000e: s/w initiated LSC MSI-X interrupts not generated; no transmit

In MSI-X mode when an IMPI SoL session was active (i.e. the PHY reset was
blocked), the LSC interrupt generated by s/w to start the watchdog which
started the transmitter was not getting fired by the hardware because bit
24 (the 'other' cause bit) also needed to be set.  Without an active SoL
session, the PHY was reset which caused the h/w to fire the LSC interrupt.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>