net/macsonic: Remove interrupt handler wrapper

On m68k, local irqs remain enabled while interrupt handlers execute.
Therefore the macsonic driver has had to disable interrupts to avoid
re-entering sonic_interrupt().

As of commit 865ad2f2 ("net/sonic: Add mutual exclusion for accessing
shared state"), sonic_interrupt() became re-entrant, and its wrapper
became redundant.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>