MFC r325436: RTF_PINNED for an interface
Allow a process to assign an IP address to local ppp interface even if kernel routing table already has a route to the address in question installed by some routing daemon (PR 223129). Also, allow loopback route deletion when stopping a VIMAGE jail (PR 222647).
PR: 222647, 223129
Reviewed by: gnn
Approved by: mav (mentor)
Differential Revision: https://reviews.freebsd.org/D12747