net: tcp: Basic exponential backoff implementation

Apply an exponentially increasing wait time between tcp retries. This
is a good balance between reacting fast to single lost packets and reduce
the network load when an outage takes a little longer. It also allows the
connection to survive a longer interruption with less retransmissions.

Update the test to accommodate for the increased socket closure timeout

Signed-off-by: Sjors Hettinga <s.a.hettinga@gmail.com>