Fix signed/unsigned comparison warnings.

diff --git a/dlls/iphlpapi/ifenum.c b/dlls/iphlpapi/ifenum.c
index e6bb8b6..aeaebdf 100644
--- a/dlls/iphlpapi/ifenum.c
+++ b/dlls/iphlpapi/ifenum.c
@@ -576,7 +576,7 @@
     if ((ioctl(fd, SIOCGIFHWADDR, &ifr)))
       ret = ERROR_INVALID_DATA;
     else {
-      int addrLen;
+      unsigned int addrLen;
 
       switch (ifr.ifr_hwaddr.sa_family)
       {