wds: add a separate --set-ip-family option

wds: add a separate --set-ip-family option

Change the current ip-family option to set the IP Family Preference
TLV in the Start Network command, and add a separate set-ip-family
option for the Set IP Family command. This is done to match how
the autoconnect and set-autoconnect options work.

Older modems don't support the Set IP Family command, and they
should use the IP Family Preference TLV. On the other hand, newer
modems, e.g., from Huawei, don't respect that TLV, and require the
use of the separate Set IP Family command.

Signed-off-by: Matti Laakso <malaakso@elisanet.fi>