Bluetooth: assert: Change printed expression to printing line and file

Change assertion messaged printed from printing expression to printing
the line and file name. This provides more context as the same
expression could be asserted upon multiple times and would then not
provide enough clarity in the message.

Also using a formatted string would save code space as we can use the
same string for all messages instead of creating a unique one for each
condition.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>