busybox: Fix of 4 CVEs

CVE-2018-1000517: fix heap buffer overflow in wget chunked decoding - CVE-2017-16544: reject terminal control sequences in shell tab completion - CVE-2018-20679: reject zero-length DHCP options and validate 4-byte option lengths - CVE-2019-5747: validate DHCPSUBNET option length before decoding...