Add support for IP blocking/filtering via file (ala SBBS ip.can)

svdm.ini IpFilterFile can be set to the path/filename of an "ip filter file",
list of IP addresses or patterns (CIDRv4 notation supported) to refuse
connections from.

This is reusing the same IP filter file logic from SBBS, so the same filter
file syntax/rules apply.
14 jobs for dailybuild_linux-x64 in 10 minutes and 19 seconds (queued for 18 seconds)
Status Name Job ID Coverage
  Build
passed jsdoor-freebsd #35865
FreeBSD

00:03:52

passed jsdoor-linux #35866
Linux

00:07:02

passed jsdoor-windows #35868
FreeBSD

00:01:53

passed sbbs-freebsd #35860
FreeBSD

00:05:26

passed sbbs-linux #35855
Linux

00:09:48

passed sbbs-windows #35858
Windows

00:05:02

passed sexpots-freebsd #35867
FreeBSD

00:00:16

passed sexpots-linux #35856
Linux

00:00:25

passed sexpots-windows #35859
Windows

00:00:28

passed syncdraw-freebsd #35863
FreeBSD

00:00:29

passed syncdraw-linux #35864
Linux

00:01:03

passed syncterm-freebsd #35861
FreeBSD

00:01:07

passed syncterm-linux #35857
Linux

00:03:06

passed syncterm-windows #35862
FreeBSD

00:01:46