change dvbpsi_packet_push to take a const data pointer

dvbpsi_packet_push does not modify the contents of the packet passed to it in
any way : thus, there is no reason for it not to be const.
external code using this function will not be affected by this change.

(cherry picked from commit 0e76e010506b088dc4a83f84086f34be86d00256)

src/dvbpsi.c

@@ -252,12 +252,12 @@ bool dvbpsi_decoder_present(dvbpsi_t *p_dvbpsi)
  *****************************************************************************
  * Injection of a TS packet into a PSI decoder.
  *****************************************************************************/
-bool dvbpsi_packet_push(dvbpsi_t *p_dvbpsi, uint8_t* p_data)
+bool dvbpsi_packet_push(dvbpsi_t *p_dvbpsi, const uint8_t* p_data)
 {
     uint8_t i_expected_counter;           /* Expected continuity counter */
     dvbpsi_psi_section_t* p_section;      /* Current section */
-    uint8_t* p_payload_pos;               /* Where in the TS packet */
-    uint8_t* p_new_pos = NULL;            /* Beginning of the new section,
+    const uint8_t* p_payload_pos;         /* Where in the TS packet */
+    const uint8_t* p_new_pos = NULL;      /* Beginning of the new section,
                                              updated to NULL when the new
                                              section is handled */
     int i_available;                      /* Byte count available in the

src/dvbpsi.h

@@ -196,7 +196,7 @@ void dvbpsi_delete(dvbpsi_t *p_dvbpsi);
  *
  * Injection of a TS packet into a PSI decoder.
  */
-bool dvbpsi_packet_push(dvbpsi_t *p_dvbpsi, uint8_t* p_data);
+bool dvbpsi_packet_push(dvbpsi_t *p_dvbpsi, const uint8_t* p_data);
 
 /*****************************************************************************
  * dvbpsi_psi_section_t