Update portnsap and port distfiles server name:
cp /etc/portsnap.conf /etc/portsnap.conf.orig
sed -i "" 's|portsnap.FreeBSD.org|portsnap3.hshh.org|' /etc/portsnap.conf
Add next line into /etc/make.conf
file:
MASTER_SITE_OVERRIDE?=http://mirrors.ustc.edu.cn/freebsd-ports/distfiles/${DIST_SUBDIR}/