Resume parsing proc connections via split

While back I put quite a bit of elbow grease into speeding up connection
resolution. To this end commit 8da78a9f squeezed out a 30% improvement by
parsing proc contents using indices rather than split.

I was torn at the time since this made our code quite a bit more verbose and
fragile, but all things being equal seemed worth the speed boost. However, in
digging into connection resolution discrepancies Toralf spotted that when a
relay has at least 10,000 connections the first column (sl) gets wider,
throwing our parser off.

Proc is clearly intended to be parsed via delimiters, not static indices. As
such largely reverting commit 8da78a9f.