(ITS#7132) syncrepl uses freed naming attrs

Full_Name: Hallvard B Furuseth Version: 2.4.28, master OS: Linux x86_64 URL: Submission from: (NULL) (129.240.203.186) Submitted by: hallvard syncrepl_entry() reads naming attrs in an entry saved by dn_callback() in an internal search, after the search returned and released the entry. Found with valgrind and -DSLAP_NO_SL_MALLOC in test017 with mdb. Fixing.