The ip_addr_t of lwIP has support for both IPv6 and IPv4 addresses.
Some lwIP commans is directly accessing the internal addr field of the
ip_addr_t instead of using ipaddr helper functions.

Change to use ipaddr helper functions where appropriate to remove direct
access of the internal addr field. Also change a few instances from ip4
to the version less ipaddr helpers.

There is no intended functional change, besides the change from using
ip4 addr helper to using version less ipaddr helper.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Jerome Forissier <jerome.forissier@arm.com>

The legacy network stack sets net_try_count to 1 at the beginning of the
net_loop() function. This is required for net_start_again() to work
properly. Therefore, set the variable accordingly in the do_ping()
function when NET_LWIP=y. This fixes an issue where a ping to an
unreachable destination would run twice on the same network device. For
example with qemu_arm64_lwip_defconfig:

 => dhcp
 DHCP client bound to address 10.0.2.15 (3 ms)
 => ping 10.0.0.1
 Using virtio-net#32 device
 ping failed; host 10.0.0.1 is not alive
 Using virtio-net#32 device
 ping failed; host 10.0.0.1 is not alive
 => QEMU: Terminated

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>

Update the ping command so that a host name is accepted in addition to
an IP address, provided DNS support is enabled.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>

Move each command in cmd/net-lwip.c into its own file
(cmd/lwip/${cmd}.c).

Suggested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>

Prepare to split the ping command from cmd/net-lwip.c by moving the
implementation from net/lwip/dns.c to cmd/lwip.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>