mv: Set file flags after setting file times

Some file flags prevent modification of file times, so they should be
set later. This matches NetBSD's behaviour.

Reviewed by: markj
MFC after: 1 week
Pull Request: https://github.com/freebsd/freebsd-src/pull/1138

(cherry picked from commit 428f86fd2ff1fd2b073d556fac273c8c7f457376)