DARWIN: Fix processing using rx_ifaddr_* macros in afsi_SetServerIPRank()

DARWIN: Fix processing using rx_ifaddr_* macros in afsi_SetServerIPRank()

The macros rx_ifaddr_address, rx_ifaddr_netmask, and rx_ifaddr_dstaddress
all expand to a call to memcpy() which returns the destination address as
its return value. The test in the DARWIN version of afsi_SetServerIPRank()
for completion when using this macro, however, seems to assume that success
returns zero, which is wrong and results in myAddr, subnetmask, and
myDstaddr always being set to zero. This patch corrects this behaviour.

Change-Id: I66f5c790d8c55b359e3550b6d71f3abe040a2820
Reviewed-on: http://gerrit.openafs.org/3401
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>