proxy: {TCP,UDP} multi-port handling
proxy: {TCP,UDP} multi-port handling

We support two cases:

1. Let |ports| = |ports| then for i, j in {0, ..., n}
   forward port_i -> port_j
2. Let |ports| = |ports| and |ports| = 1 then for i in {0, ..., n}
   forward port_i -> port

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

mjeanson/lxd,Skarlso/lxd,hallyn/lxd,Skarlso/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,mjeanson/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,atxwebs/lxd,Skarlso/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,mjeanson/lxd,hallyn/lxd,Skarlso/lxd,lxc/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd