multiple `-net user` arguments generated when using network redirections

[ckuethe]

Vaguely related to #54 - after editing my .aqemu file to remove the extraneous..., aqemu computes multiple -net user arguments when using network redirections which causes QEMU emulator version 2.11.1(Debian 1:2.11+dfsg-1ubuntu7.6) to spin.

    -net nic,vlan=0,model=e1000 \
    -net user,vlan=0 \
    -net user,hostfwd=tcp::2022-:22 \

If I collapse the user net configuration to -net user,vlan=0,hostfwd=tcp::2022-:22 redirection works, qemu doesn't hang, and I can ssh into my VM.