MDEV-25328: --innodb command line option causes mariabackup to fail

This patch fixes an issue with launching mariabackup during SST
(when used with Galera), when during bootstrap mariabackup receives
the "--innodb" option, which is incorrectly interpreted as shortcut
for "--innodb-force-recovery". This patch does not require separate
test for mtr, as the problem is visible in general testing on
buildbot.

extra/mariabackup/xtrabackup.cc

@@ -6622,6 +6622,8 @@ int main(int argc, char **argv)
 {
 	char **client_defaults, **server_defaults;
 
+	my_getopt_prefix_matching= 0;
+
 	if (get_exepath(mariabackup_exe,FN_REFLEN, argv[0]))
     strncpy(mariabackup_exe,argv[0], FN_REFLEN-1);