Lint: Add linter for log statements

[oncilla]

Adds linter for log statements.
Also, fix all the places the linter flagged in the codebase.

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This change is 

[lukedirtwalker]

💯

Reviewed 5 of 5 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

a discussion (no related file):
hm I just realized that the case in the BR is not catched: https://github.com/scionproto/scion/blob/master/go/border/rctrl/ifstate.go#L45

But it's certainly better than nothing.

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[oncilla]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

[oncilla]

a discussion (no related file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

hm I just realized that the case in the BR is not catched: https://github.com/scionproto/scion/blob/master/go/border/rctrl/ifstate.go#L45

But it's certainly better than nothing.

created oncilla/gochecks#6 to track this

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