Fix wrong interface match when using the "iface-regex" option

[spideyfusion]

Description

We've noticed that when using the iface-regex CLI option, the wrong interface would get selected even though it was the only interface matching the IP specified in the regex pattern.

Upon closer inspection of the code, it looks like attempting to break away from the main for loop only exits the switch statement.

This makes it so when there is a regex match, as we continue iterating through all the available network interfaces, the last element will always get stored since ifaceToMatch is passed by reference.

Scenario

Interface list

3: enp3s0f1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether d0:50:99:fe:29:21 brd ff:ff:ff:ff:ff:ff
    inet 172.16.15.2/16 brd 172.16.255.255 scope global enp3s0f1
       valid_lft forever preferred_lft forever

...

166872: vethf134d2d5@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master cni0 state UP group default
    link/ether 82:82:b4:8d:b5:bc brd ff:ff:ff:ff:ff:ff link-netns cni-206b7340-a74b-2ae2-999d-6f4ecc4a3398
    inet6 fe80::8082:b4ff:fe8d:b5bc/64 scope link
       valid_lft forever preferred_lft forever

Launch options used

./flanneld --ip-masq --kube-subnet-mgr --iface-regex=^172\\.16\\.

Expected result

I0207 09:15:43.273911       1 main.go:698] Using interface with name enp3s0f1 and address 172.16.15.2
I0207 09:15:43.273930       1 main.go:720] Defaulting external address to interface address (172.16.15.2)

Actual result

I0207 09:15:43.273911       1 main.go:698] Using interface with name vethf134d2d5 and address 172.16.15.2
I0207 09:15:43.273930       1 main.go:720] Defaulting external address to interface address (172.16.15.2)

Todos

• Tests
• Documentation
• Release note

Release Note

None required