Pick interfaces smarter

[dddddai]

In calico ipip mode, each pod has tunl0 inside
projectcalico/calico#2156 (comment)

For example:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN qlen 1
    link/ipip 0.0.0.0 brd 0.0.0.0
4: eth0@if31: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1480 qdisc noqueue state UP
    link/ether 7a:9e:e8:28:b2:6f brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 100.103.244.106/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::789e:e8ff:fe28:b26f/64 scope link
       valid_lft forever preferred_lft forever

This patch is aimed to make the interface selection a bit smarter

[mergify]

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[codecov-commenter]

Codecov Report

Merging #187 (a92ba58) into main (9229c2b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #187   +/-   ##
=======================================
  Coverage   17.11%   17.11%           
=======================================
  Files           5        5           
  Lines         368      368           
=======================================
  Hits           63       63           
  Misses        295      295           
  Partials       10       10           

Flag	Coverage Δ
unittests	17.11% <ø> (ø)

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