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: Bas van Sisseren <bas@quarantainenet.nl>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/net/slirp.c b/net/slirp.c
index b3f35d5..124e953 100644
--- a/net/slirp.c
+++ b/net/slirp.c
@@ -212,14 +212,6 @@
         return -1;
     }
 
-    if (vdhcp_start && !inet_aton(vdhcp_start, &dhcp)) {
-        return -1;
-    }
-    if ((dhcp.s_addr & mask.s_addr) != net.s_addr ||
-        dhcp.s_addr == host.s_addr || dhcp.s_addr == dns.s_addr) {
-        return -1;
-    }
-
     if (vnameserver && !inet_aton(vnameserver, &dns)) {
         return -1;
     }
@@ -228,6 +220,14 @@
         return -1;
     }
 
+    if (vdhcp_start && !inet_aton(vdhcp_start, &dhcp)) {
+        return -1;
+    }
+    if ((dhcp.s_addr & mask.s_addr) != net.s_addr ||
+        dhcp.s_addr == host.s_addr || dhcp.s_addr == dns.s_addr) {
+        return -1;
+    }
+
 #ifndef _WIN32
     if (vsmbserver && !inet_aton(vsmbserver, &smbsrv)) {
         return -1;