Fix mistranslation for the expression, "during getting up to speed with
FreeBSD firewalling".

Previous translation restricted the situation to the time when OS
is upgraded, and expressed the following in Japanese:
"while people is catching up with firewall features changed by new
FreeBSD release."

New translation does not, and expresses the following in Japanese:
"while people is getting used to FreeBSD firewalling."

Submitted by:AMAKAWA Shuhei <sa264@cam.ac.uk>