tests: net: socket: reuseaddr_reuseport: Fix userspace testing

net_context_foreach() is not a systemcall, therefore should not be used
from userspace threads. Usage of this API made SO_REUSADDR/SO_REUSEPORT
userspace tests unfunctional (crashing).

Fix this by using CONFIG_NET_TCP_TIME_WAIT_DELAY instead for tests that
involve TCP connections. Other tests don't really need to wait as
there's no teardown delay on UDP or unconnected TCP contexts.

Additionally, remove the platform exclude for qemu_x86 platform, as this
was the sole reason the tests were crashing on that platform.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>