Reverse USB Tethering
adb shell netcfg usb0 up
adb shell netcfg usb0 dhcp
adb shell route add default gw X.X.X.X dev usb0
adb shell setprop ro.kernel.android.ndns 2
adb shell setprop net.dns1 188.8.131.52
adb shell setprop net.dns2 184.108.40.206
adb shell setprop "net.gprs.http-proxy" ""
adb shell setprop net.usb0.dns1 220.127.116.11
adb shell setprop net.usb0.dns2 18.104.22.168
Do not copy and paste these commands. Read them and see if you can understand what they are accomplishing and modify them to suit your needs. You are routing over USB.
ifconfig eth0 0.0.0.0
ifconfig usb0 0.0.0.0
brctl addbr br0
brctl addif br0 eth0
brctl addif br0 usb0
ifconfig br0 up
Do not copy and paste these commands. Since you don't have network access on your PC, you will not need to make a bridge, but if you ever add a NIC, then you may want to create a bridge.