feat(dns): add an option device to set SO_BINDTODEVICE

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

dns.lua

@@ -442,6 +442,7 @@ end
     nameservers: a list of nameservers to be used. Each nameserver entry can be either a
                 single hostname string or a table holding both the hostname string and the port number.
     mark: a number used to set SO_MARK to socket
+    device: a string used to set SO_BINDTODEVICE to socket
 --]]
 function M.query(qname, opts)
     if string.byte(qname, 1) == string.byte('.') or #qname > 255 then
@@ -526,6 +527,10 @@ function M.query(qname, opts)
             s:setoption('mark', opts.mark)
         end
 
+        if opts.device then
+            s:setoption('bindtodevice', opts.device)
+        end
+
         answers, err = query(s, id, req, nameserver)
         s:close()
 

socket.lua

@@ -178,6 +178,10 @@ function M.socket(family, domain, protocol, options)
         sock:setoption('mark', options.mark)
     end
 
+    if options.device then
+        sock:setoption('bindtodevice', options.device)
+    end
+
     return setmetatable(o, metatable)
 end