Fix astcanary startup problem due to wrong pid value from before daemon call

When Asterisk forks itself into the background via a call to daemon, it must
re-set the pid value of the new process. Otherwise, astcanary gets the pid
value of the process before the fork, which prevents it from running. Asterisk
eventually starts lowering its priority, as it can no longer communicate
with the proverbial canary in the coal mine.

This patch ensures that the correct process identifier is used by astcanary.

Note that this is getting committed to 10 as a regression fix.

(closes issue ASTERISK-20947)
Reported by: Jakob Hirsch
Tested by: mjordan
patches:
  asterisk-10.12.0.astcanary_ppid.diff uploaded by Jakob Hirsch (license 6113)
........

Merged revisions 379509 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@379510 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/asterisk.c

@@ -3788,6 +3788,8 @@ int main(int argc, char *argv[])
 #ifndef HAVE_SBIN_LAUNCHD
 		if (daemon(1, 0) < 0) {
 			fprintf(stderr, "daemon() failed: %s\n", strerror(errno));
+		} else {
+			ast_mainpid = getpid();
 		}
 #else
 		fprintf(stderr, "Mac OS X detected.  Use 'launchctl load /Library/LaunchDaemon/org.asterisk.asterisk.plist'.\n");
@@ -3839,11 +3841,10 @@ int main(int argc, char *argv[])
 	}
 
 	/* Blindly write the PID file. */
-	ast_mainpid = getpid();
 	unlink(ast_config_AST_PID);
 	f = fopen(ast_config_AST_PID, "w");
 	if (f) {
-		fprintf(f, "%ld\n", (long)getpid());
+		fprintf(f, "%ld\n", (long)ast_mainpid);
 		fclose(f);
 	} else {
 		fprintf(stderr, "Unable to open pid file '%s': %s\n", ast_config_AST_PID, strerror(errno));