Hook up affinity-setting for U3/U4 MSI interrupt sources.

Tested on Quad G5 with myri10ge.
Signed-off-by: NOlof Johansson <olof@lixom.net>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>