This adds parameters h2_rapid_reset_limit and h2_rapid_reset_period,
which govern the rate of which we permit clients to reset streams.

If the limit is exceeded the connection is closed.

Related to: varnishcache#1851

Conflicts:
	include/tbl/params.h

Conflicts:
	bin/varnishd/VSC_main.vsc
	include/tbl/sess_close.h

Only RST frames received earlier than this duration will be considered
rapid.

Includes backports of the following upstream doc-touchups:
- 151f4d5
- 46d4f82

Conflicts:
	include/tbl/params.h

backport of f820f80

Conflicts:
	include/tbl/params.h

Backport of 2cfb561 and 1a406e3

Conflicts:
	bin/varnishtest/vmods.h
	configure.ac
	lib/Makefile.am

we can not make the parameter const because API.