net: bcmgenet: tweak init_umac()

Use more meaningful variable names int0_enable and int1_enable when
enabling bcmgenet interrupts.

For Rx default queue interrupts, use:
UMAC_IRQ_RXDMA_BDONE | UMAC_IRQ_RXDMA_PDONE

For Tx default queue interrupts, use:
UMAC_IRQ_TXDMA_BDONE | UMAC_IRQ_TXDMA_PDONE

Signed-off-by: Petri Gynther <pgynther@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>