HSR/PRP: Add -P flag for dissecting PRP trailer

To avoid dissecting PRP trailer when we aren't using PRP.

Author: cappe987

netdissect.h

@@ -214,6 +214,7 @@ struct netdissect_options {
   int ndo_Aflag;		/* print packet only in ASCII observing TAB,
 				 * LF, CR and SPACE as graphical chars
 				 */
+  int ndo_Pflag;		/* print packet in hex/ASCII */
   int ndo_Hflag;		/* dissect 802.11s draft mesh standard */
   const char *ndo_protocol;	/* protocol */
   jmp_buf ndo_early_end;	/* jmp_buf for setjmp()/longjmp() */

print-ether.c

@@ -306,7 +306,7 @@ ether_common_print(netdissect_options *ndo, const u_char *p, u_int length,
 		hdrlen += 6;
 	}
 
-	if (caplen >= 6) {
+	if (ndo->ndo_Pflag && caplen >= 6) {
 		prp_suffix = GET_BE_U_2(p + caplen - 2);
 		if (prp_suffix == 0x88fb) {
 			prp_print(ndo, p, caplen);

tcpdump.c

@@ -672,7 +672,7 @@ show_remote_devices_and_exit(void)
 #define U_FLAG
 #endif
 
-#define SHORTOPTS "aAb" B_FLAG "c:C:d" D_FLAG "eE:fF:G:hHi:" I_FLAG j_FLAG J_FLAG "KlLm:M:nNOpq" Q_FLAG "r:s:StT:u" U_FLAG "vV:w:W:xXy:Yz:Z:#"
+#define SHORTOPTS "aAb" B_FLAG "c:C:d" D_FLAG "eE:fF:G:hHi:" I_FLAG j_FLAG J_FLAG "KlLm:M:nNOpPq" Q_FLAG "r:s:StT:u" U_FLAG "vV:w:W:xXy:Yz:Z:#"
 
 /*
  * Long options.
@@ -1738,6 +1738,10 @@ main(int argc, char **argv)
 			++pflag;
 			break;
 
+		case 'P':
+			++ndo->ndo_Pflag;
+			break;
+
 		case 'q':
 			++ndo->ndo_qflag;
 			++ndo->ndo_suppress_default_print;

tests/TESTLIST

@@ -839,4 +839,4 @@ lsp-ping-timestamp	lsp-ping-timestamp.pcap		lsp-ping-timestamp.out	-vv
 
 # HSR/PRP tests
 hsr		hsr.pcap	hsr.out		-e
-prp		prp.pcap	prp.out		-e
+prp		prp.pcap	prp.out		-e -P