nwfilter: drop dead code

Commit cb022152 went overboard and introduced a dead conditional
while trying to get rid of a potential NULL dereference.

* src/nwfilter/nwfilter_dhcpsnoop.c (virNWFilterSnoopReqNew):
Remove redundant conditional.

src/nwfilter/nwfilter_dhcpsnoop.c

@@ -573,7 +573,7 @@ virNWFilterSnoopReqNew(const char *ifkey)
 {
     virNWFilterSnoopReqPtr req;
 
-    if (ifkey == NULL || (ifkey && (strlen(ifkey) != VIR_IFKEY_LEN - 1))) {
+    if (ifkey == NULL || strlen(ifkey) != VIR_IFKEY_LEN - 1) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("virNWFilterSnoopReqNew called with invalid "
                          "key \"%s\" (%zu)"),