MFC r284245:

MFC r284245:
Fix a callout race condition introduced in TCP timers callouts with r281599.
In TCP timer context, it is not enough to check callout_stop() return value
to decide if a callout is still running or not, previous callout_reset()
return values have also to be checked.

git-svn-id: svn://svn.freebsd.org/base/stable/10@284261 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f