Bluetooth: Mesh: Fix discarding messages with many segments

The code for checking space in the Friend queue was faulty in the case
that we receive a message with more segments than the configured Friend
Queue size. This is not an issue for the default configuration but
still a possible one. Move the check for exceeding Friend Queue Size
to the per-LPN function, so that bt_mesh_friend_queue_has_space()
iterates all LPNs before delivering its verdict. This allows us to
return success in case no LPN matched (which is how the code was
intended to work).

Fixes #18522

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>