Allows to dynamically change the MutexProfileFraction to enable and
disable mutex profiling. It should be very useful for detecting
deadlocks, lock contention and general concurrency problems.

How to use:
To enable run: curl -X POST -v 'localhost:5001/debug/pprof-mutex/?fraction=10
To disable: curl -X POST -v 'localhost:5001/debug/pprof-mutex/?fraction=0'

Fraction defines which fraction of events will be profiled. Higher it is
the lower performance impact but less reliable the result.

To fetch the result use:
go tool pprof $PATH_TO_IPFS_BIN http://localhost:5001/debug/pprof/mutex

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>