Merge FreeBSD SA-20:21-30 EN-20:17-18

Fix memory corruption in USB network device drivers. [SA-20:21.usb_net]
Fix multiple vulnerabilities in sqlite3. [SA-20:22.sqlite]
Fix sendmsg(2) privilege escalation. [SA-20:23.sendmsg]
Fix IPv6 Hop-by-Hop options use-after-free. [SA-20:24.ipv6]
Fix SCTP socket use-after-free. [SA-20:25.sctp]
Fix dhclient heap overflow. [SA-20:26.dhclient]
Fix ure device driver susceptible to packet-in-packet attack. [SA-20:27.ure]
Fix bhyve privilege escalation via VMCS access. [SA-20:28.bhyve_vmcs]
Fix bhyve SVM guest escape. [SA-20:29.bhyve_svm]
Fix ftpd privilege escalation via ftpchroot. [SA-20:30.ftpd]

Fix FreeBSD Linux ABI kernel panic. [EN-20:17.linuxthread]
Fix getfsstat compatibility system call panic. [EN-20:18.getfsstat]