floss: Fix empty peer name issue when RNR is skipped

Peer devices with BTM_SEC_NAME_KNOWN flag set have their
device names stored in sec_bd_name. If RNR is skipped
for this kind of device, bat_dm_search_cb.peer_name would
be empty and sec_bd_name shall be used instead.
Therefore, this patch uses bta_dm_get_remname() to fill up
the tBTA_DM_MSG in bta_dm_discover_device() and applies the
same indirection layer to similar situations for consistency.

Bug: 265433346
Bug: 260598196
Tag: #floss
Test: Manual test - pairing with classic keyboard

Change-Id: I7a297ff9a53ccbd6f3b9283e61ed208b000e6678