tcpdump: plug a memory leak.

If the -V flag is used, and not all files in the -V file have the same
link-layer type, when the filter is recompiled for a new link-layer
type, the old filter program is leaked.  Free the old filter before
compiling the new filter.

(cherry picked from commit 9904bbb)

tcpdump.c

@@ -2654,6 +2654,8 @@ DIAG_ON_ASSIGN_ENUM
 					 */
 					dlt = new_dlt;
 					ndo->ndo_if_printer = get_if_printer(dlt);
+					/* Free the old filter */
+					pcap_freecode(&fcode);
 					if (pcap_compile(pd, &fcode, cmdbuf, Oflag, netmask) < 0)
 						error("%s", pcap_geterr(pd));
 				}