tests: net: sockets: tls: Add test verifying send() after close

Add test case verifying that send() returns an error when called after
TLS session has been closed.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
(cherry picked from commit b920793e9bfe35909d71beb84d62a87537f15d75)
1 file changed