pcapint_do_addexit() fills the error buffer. [skip ci]

Do not do it in pcap_activate_bpf(), update the comments.

Author: infrastation

pcap-bpf.c

@@ -2084,9 +2084,8 @@ pcap_activate_bpf(pcap_t *p)
 				/*
 				 * "atexit()" failed; don't create the
 				 * interface, just give up.
+				 * p->errbuf has already been filled.
 				 */
-				snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
-				     "atexit failed");
 				close(s);
 				status = PCAP_ERROR;
 				goto bad;
@@ -3220,6 +3219,7 @@ monitor_mode(pcap_t *p, int set)
 				/*
 				 * "atexit()" failed; don't put the interface
 				 * in monitor mode, just give up.
+				 * p->errbuf has already been filled.
 				 */
 				close(sock);
 				return (PCAP_ERROR);

pcap-linux.c

@@ -5031,6 +5031,7 @@ enter_rfmon_mode(pcap_t *handle, int sock_fd, const char *device)
 		/*
 		 * "atexit()" failed; don't put the interface
 		 * in rfmon mode, just give up.
+		 * handle->errbuf has already been filled.
 		 */
 		del_mon_if(handle, sock_fd, &nlstate, device,
 		    handlep->mondevice);