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.

Reviewed-on: http://gerrit.openafs.org/3401
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 8fa01c4d602fac6d5d81b119d0593f02087e4302)
Change-Id: If4a47f57a804a2492659d74a5e930f4a962f1748
Reviewed-on: http://gerrit.openafs.org/3451