This commit migrates softirqs to use kernel tracepoints instead of
kprobes. Because tracepoints only provide the vector number and not
the function name, we use a conversion table, which is borrowed from
kernel/softirq.c, to translate the vector number to a display name.
This table is expected to be fairly stable. Notably, new names have
not been added since approximately 2009, and the last rename (without
adding or removing a name) was in 2014.

Resolves #1031.