MINOR: conn_stream: remove the now unused CS_FL_ADDR_*_SET flags

MINOR: conn_stream: remove the now unused CS_FL_ADDR_*_SET flags

These flags indicate that the ->src or ->dst field in the conn_stream
is not null, which is something the caller already sees (and even tests
from the two sets of functions that set them). They maintain some burden
because an agent trying to set a source or destination has to manually
set the flags in addition to setting the pointer, so they provide no
value anymore, let's drop them.