pppd: update to 2.4.8

pppd: update to 2.4.8

78cd384 Update README and patchlevel.h for 2.4.8 release
5d03403 pppd: Avoid use of strnlen (and strlen) in vslprintf
a1e950a pppd: Fix IPv6 default route code for Solaris
ca5e61b plugins/rp-pppoe: Make tag parsing loop condition more accurate
c10c3c7 pppd: Make sure word read from options file is null-terminated
b311e98 pppd: Limit memory accessed by string formats with max length specified
3ea9de9 pppd: Eliminate some more compiler warnings
57edb1a pppd: Include time.h header before using time_t
09f695f pppd: Don't free static string
03104ba pppd.h: Add missing headers
388597e pppd: Add defaultroute6 and related options
66ce4ba pppd: Avoid declarations within statements in main.c
5637180 pppd: Fix `ifname` option in case of multilink (#105)
d00f8a0 pppd: Fix variable reference syntax in Makefile.linux
b6b4d28 pppd: Check tdb pointer before closing

Signed-off-by: DENG Qingfang <dengqf6@mail2.sysu.edu.cn>