/etc/init.d/networking.sh multi-interfaces handling update

Use case:
    eth0 + eth1 are connected to a dhcp server (not necessarily the same).
Observed behavior:
    eth1 receives static ip rather than dhcp's.
Expected behavior:
    Both eth0 + eth1 should receive dhcp's ip addresses.
TODO:
    Revise default hostname behavior on multiple interfaces system.
Test setup:
    eth0 and eth1 are connected to a single DHCP servers with different
    subnets (eth1 and eth2)
    Mellanox ONIE PPC460EX platform
Tests:
    "/etc/init.d/networking.sh start" on:
    eth0 connected , eth1 disconnected
    eth0 disconnected , eth1 disconnected
    eth0 disconnected , eth1 connected
    eth0 connected , eth1 connected
Tests log:
MLNX460:/ #  /etc/init.d/networking.sh start ; echo $?
ONIE: Using DHCPv4 addr: eth0: 192.168.0.240 / 255.255.255.0
ONIE: Using default IPv4 addr: eth1: 192.168.3.11/255.255.255.0
0
MLNX460:/ #  /etc/init.d/networking.sh start ; echo $?
ONIE: Using default IPv4 addr: eth0: 192.168.3.10/255.255.255.0
ONIE: Using default IPv4 addr: eth1: 192.168.3.11/255.255.255.0
0
MLNX460:/ #  /etc/init.d/networking.sh start ; echo $?
ONIE: Using default IPv4 addr: eth0: 192.168.3.10/255.255.255.0
ONIE: Using DHCPv4 addr: eth1: 192.168.10.195 / 255.255.255.0
0
MLNX460:/ #  /etc/init.d/networking.sh start ; echo $?
ONIE: Using DHCPv4 addr: eth0: 192.168.0.240 / 255.255.255.0
ONIE: Using DHCPv4 addr: eth1: 192.168.10.195 / 255.255.255.0
0
MLNX460:/ #

Reviewed by: Curt Brune <curt@cumulusnetworks.com>
Reviewed by: Itai Baz <itaib@mellanox.com>
Signed-off-by: Doron Tsur <doront@mellanox.com>