udhcpc: support for -O <option>.

Two important notes:
* nissrv and nisdomain are not requested by default anymore!
* inconsistency between "XXXsvr" and "XXsrv" in option names resolved,
  all are "XXXsrv" now.

function                                             old     new   delta
udhcpc_main                                         2494    2600    +106
packed_usage                                       23023   23067     +44
add_requests                                          91     119     +28
static.udhcpc_longopts                               209     226     +17
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 195/0)             Total: 195 bytes

1 files changed, 8 insertions, 3 deletions

diff --git a/networking/udhcp/clientpacket.c b/networking/udhcp/clientpacket.c
index 406fe340a..54f3f0e49 100644
--- a/networking/udhcp/clientpacket.c
+++ b/networking/udhcp/clientpacket.c
@@ -57,13 +57,18 @@ static void init_packet(struct dhcpMessage *packet, char type)
  * goes towards the head of the packet. */
 static void add_requests(struct dhcpMessage *packet)
 {
+        uint8_t c;
         int end = end_option(packet->options);
         int i, len = 0;
 
         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
-        for (i = 0; dhcp_options[i].code; i++)
-                if (dhcp_options[i].flags & OPTION_REQ)
-                        packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
+        for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
+                if (dhcp_options[i].flags & OPTION_REQ
+                 || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
+                ) {
+                        packet->options[end + OPT_DATA + len++] = c;
+                }
+        }
         packet->options[end + OPT_LEN] = len;
         packet->options[end + OPT_DATA + len] = DHCP_END;