apps/nshlib: fix warning by tool converity report

uninit_use_in_call addr before call netlib_set_ipv4addr at line 780

Signed-off-by: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>

nshlib/nsh_netcmds.c

@@ -776,6 +776,10 @@ int cmd_ifconfig(FAR struct nsh_vtbl_s *vtbl, int argc, char **argv)
               gip         = addr.s_addr;
             }
         }
+      else
+        {
+          addr.s_addr = 0;
+        }
 
       netlib_set_ipv4addr(ifname, &addr);
     }