samples: net: irc_bot: add IPv4 support

NOTE: You must set CONFIG_NET_IPV6=n in the project .conf file for
the CONFIG_NET_IPV4 setting to take effect.

Only 1 IP connection is active at a time.  And when both are active
CONFIG_NET_IPV6 takes precedence.

Change-Id: I34a75f8d44db986810648d82a65d2ed29fc9a940
Signed-off-by: Michael Scott <michael.scott@linaro.org>