supplicant:  Allow user-defined defaults for Interworking network blocks.

This way users can still configure the HT over-rides and some other
constraints that Interworking has no interest or ability to configure.

Example config file (to disable HT-40 on an Interworking/HS20 interface):

ctrl_interface=/var/run/wpa_supplicant
fast_reauth=1

interworking=1
auto_interworking=1
access_network_type=0

hs20=1

bss_max_count=2000
network={
    interworking_defaults=1
    disable_ht=0
    disable_ht40=1
    disable_sgi=0
    ht_mcs=""
    disable_max_amsdu=-1
    ampdu_factor=-1
    ampdu_density=-1

}

cred={
    username="client2"
    password="lanforge"
    ca_cert="/home/lanforge/ca.pem"
    private_key="/home/lanforge/client.p12"
    private_key_passwd="lanforge"
    realm="lanforge.org"
    domain="lanforge.org"
    eap=TLS

}

Signed-hostap: Ben Greear <greearb@candelatech.com>