chg: usr: Fix network manager issue when both success and timeout callbacks can be...

This commit simplifies code flow in the tls_cycle_input() and makes
the incoming data processing similar to that in TCP DNS. In
particular, now we decipher all the the incoming data before making a
single isc__nm_process_sock_buffer() call. Previously we would try to
decipher data bit-by-bit before trying to process the deciphered bit
via isc__nm_process_sock_buffer(). Doing like before made the code
much less predictable, in particular in the areas like when reading is
paused or resumed.

The newer approach also allowed us to get rid of some old kludges.

Closes #5247

Merge branch '5247-unexpected-callbacks' into 'bind-9.18'

See merge request isc-projects/bind9!10294