Source for "src_dst_swap"

                #define IP_SRC_ADDR     12
                #define IP_DST_ADDR     16
                #define TCP_SRC_PORT    20
                #define TCP_DST_PORT    22
                #define TCP_SEQ_NUM     24

                #define TCP_ACK_NUM     28
                #define SCRATCH         15

                ld [IP_SRC_ADDR:4];     // load src IP address
                st M[SCRATCH];          // store to scratch location
                ld [IP_DST_ADDR: 4];    // load dst IP address
                st [IP_SRC_ADDR: 4];    // store to src IP location in packet
                ld M[SCRATCH];          // load scratch location
                st [IP_DST_ADDR: 4];    // store to dst IP location in packet

                ld [TCP_SRC_PORT: 2];   // load src port
                st M[SCRATCH];          // store to scratch location
                ld [TCP_DST_PORT: 2];   // load dst port
                st [TCP_SRC_PORT: 2];   // store to src port location in packet
                ld M[SCRATCH];          // load scratch location
                st [TCP_DST_PORT: 2];   // store to dst

                ld [TCP_SEQ_NUM:4];	// load sequence number
                st M[SCRATCH];		// store to scratch location
                ld [TCP_ACK_NUM: 4];	// load last ack'd sequence number
                st [TCP_SEQ_NUM: 4];	// store as sequence number
                ld M[SCRATCH];		// load scratch location
                st [TCP_ACK_NUM: 4];	// store as last ack'd sequence number