fix -net user checks by reordering checks

reorder slirp config options. first check the dns-server-address,
then check the first-dhcp-address. the original code was comparing
the first-dhcp-address with the default dns-server-address, not
the configured dns-server-address.
Signed-off-by: NBas van Sisseren <bas@quarantainenet.nl>
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>

net/slirp.c

@@ -212,19 +212,19 @@ static int net_slirp_init(NetClientState *peer, const char *model,
         return -1;
     }
 
-    if (vdhcp_start && !inet_aton(vdhcp_start, &dhcp)) {
+    if (vnameserver && !inet_aton(vnameserver, &dns)) {
         return -1;
     }
-    if ((dhcp.s_addr & mask.s_addr) != net.s_addr ||
-        dhcp.s_addr == host.s_addr || dhcp.s_addr == dns.s_addr) {
+    if ((dns.s_addr & mask.s_addr) != net.s_addr ||
+        dns.s_addr == host.s_addr) {
         return -1;
     }
 
-    if (vnameserver && !inet_aton(vnameserver, &dns)) {
+    if (vdhcp_start && !inet_aton(vdhcp_start, &dhcp)) {
         return -1;
     }
-    if ((dns.s_addr & mask.s_addr) != net.s_addr ||
-        dns.s_addr == host.s_addr) {
+    if ((dhcp.s_addr & mask.s_addr) != net.s_addr ||
+        dhcp.s_addr == host.s_addr || dhcp.s_addr == dns.s_addr) {
         return -1;
     }