Separate service discovery and read remote name callback

Long time ago someone decided that using one callback for service
search and device search is good idea.
Turns out it's a bad idea that's causing service discovery callback when
name read callback comes back. This, in turn, causes profiles to not
connect properly.
To fix this, separate event is introduced for name read.

Test: atest net_test_btif_stack
Bug: 311217960
Change-Id: I343a585ffcb7b6112b493af1593beca871d70c91