tutorial: make network examples work on multi-core
tutorial: make network examples work on multi-core

So far, the network server examples explained that they only work on
a single core ("-c1"). This was unduly confusing for beginners, who read
this limitation and then promptly forgot all about it :-)

So better just show, up-front, how to run the service loop on all the cores
in the simplest way, using smp::submit_to(). Then all the network server
examples will work with any number of cores.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20170314143234.20327-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

scylladb/seastar,cloudius-systems/seastar,dreamsxin/seastar,scylladb/seastar,dreamsxin/seastar,cloudius-systems/seastar,avikivity/seastar,avikivity/seastar,dreamsxin/seastar,syuu1228/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar,syuu1228/seastar