rpcd_mdssvc: initialize POSIX locking

rpcd_mdssvc: initialize POSIX locking

Otherwise the posix_pending_close_db is NULL and we crash when trying to close a
file descriptor:

   #4 /usr/lib64/samba/libdbwrap-samba4.so(dbwrap_parse_record+0xe) [0x7fbc5d05c8ae]
   #5 /usr/lib64/samba/libdbwrap-samba4.so(dbwrap_fetch_int32+0x38) [0x7fbc5d05d438]
   #6 /usr/lib64/samba/libsmbd-base-samba4.so(fd_close_posix+0x7b) [0x7fbc5e276f8b]
   #7 /usr/lib64/samba/libsmbd-base-samba4.so(+0x57900) [0x7fbc5e28a900]
   #8 /usr/lib64/samba/libsmbd-base-samba4.so(fd_close+0x68) [0x7fbc5e2b7ea8]
   #9 /usr/lib64/samba/libsmbd-base-samba4.so(+0x62608) [0x7fbc5e295608]
   #10 /usr/lib64/samba/libtalloc-samba4.so(_talloc_free+0x51b) [0x7fbc5d9f439b]
   #11 /usr/lib64/samba/vfs/fruit.so(+0xcac2) [0x7fbc45fcdac2]
   #12 /usr/lib64/samba/vfs/fruit.so(+0xcbdd) [0x7fbc45fcdbdd]
   #13 /usr/lib64/samba/vfs/fruit.so(+0xf603) [0x7fbc45fd0603]
   #14 /usr/lib64/samba/libsmbd-base-samba4.so(+0x56375) [0x7fbc5e289375]
   #15 /usr/lib64/samba/vfs/nothingtoseeherereally.so(+0x196c) [0x7fbc467f996c]
   #16 /usr/lib64/samba/vfs/streams_xattr.so(+0x51fc) [0x7fbc461e71fc]
   #17 /usr/lib64/samba/libsmbd-base-samba4.so(+0xade3a) [0x7fbc5e2e0e3a]
   #18 /usr/lib64/samba/libsmbd-base-samba4.so(create_conn_struct_cwd+0x44) [0x7fbc5e2e1cf4]
   #19 /usr/libexec/samba/rpcd_mdssvc(mds_init_ctx+0x2c3) [0x563fdac08f03]
   #20 /usr/libexec/samba/rpcd_mdssvc(_mdssvc_open+0x141) [0x563fdac0b4d1]

The corresponding open is done as part of initializing a connection_struct
object, where we chdir() and stat() the root path of the share. The stat() in
vfs_fruit causes an expensive metadata request on the path which triggers an
internal open of a pathref handle. Note that this only affects servers that have
fruit:metadata = netatalk set, which is the default unfortunately.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15354

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri Apr  7 21:12:21 UTC 2023 on atb-devel-224