Properly restore cork state when changed

Properly restore cork state when changed

These streams both need to change the corking state temporarily, but it
is important it is restored to the previous state or things might get
messed up.

For the zlib stream it would just leave things uncorked, which still
works but is less efficient.

But for the TLS stream it might make things very unresponsive as the
corking might be left on permanently, delaying packets indefinitely.