udhcp: MAC_BCAST_ADDR and blank_chaddr are in fact constant, move to rodata.
a few global variables reduced to smallints
function                                             old     new   delta
add_lease                                             75     227    +152
static.blank_chaddr                                    -      16     +16
MAC_BCAST_ADDR                                         -       6      +6
sockfd                                                 4       8      +4
udhcp_run_script                                    1153    1155      +2
state                                                  8       5      -3
listen_mode                                            4       1      -3
perform_release                                      152     148      -4
fd                                                     8       4      -4
blank_chaddr                                          16       -     -16
udhcpc_main                                         2518    2497     -21
.rodata                                           131864  131832     -32
oldest_expired_lease                                  61       -     -61
clear_lease                                          127       -    -127
------------------------------------------------------------------------------
(add/remove: 2/3 grow/shrink: 3/6 up/down: 180/-271)          Total: -91 bytes

diff --git a/networking/udhcp/common.h b/networking/udhcp/common.h
index 00890ac..6c0db5b 100644
--- a/networking/udhcp/common.h
+++ b/networking/udhcp/common.h
@@ -14,8 +14,7 @@
 
 #define DEFAULT_SCRIPT  "/usr/share/udhcpc/default.script"
 
-#define COMBINED_BINARY
-
+extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */
 
 /*** packet.h ***/
 
@@ -52,7 +51,8 @@
 uint16_t udhcp_checksum(void *addr, int count);
 int udhcp_raw_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
-		uint32_t dest_ip, int dest_port, uint8_t *dest_arp, int ifindex);
+		uint32_t dest_ip, int dest_port,
+		const uint8_t *dest_arp, int ifindex);
 int udhcp_kernel_packet(struct dhcpMessage *payload,
 		uint32_t source_ip, int source_port,
 		uint32_t dest_ip, int dest_port);