tests: net: all: Fix assignments to old TIME_WAIT Kconfig symbols

CONFIG_NET_TCP_{TIME_WAIT,2MSL_TIME} were replaced by
CONFIG_NET_TCP_TIME_WAIT_DELAY in commit 89f57c22 ("net:tcp: Define
single condig option for TIME_WAIT delay"), which also switched from
seconds to milliseconds for specifying the delay.

Remove the old assignments and set the new symbol to give the same
behavior as before.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>