Properly copy/remove the device state cache flag over a masquerade.

In r378303 the AST_FLAG_DISABLE_DEVSTATE_CACHE flag was added that tells
the devstate system to not cache states for non-real devices. However,
when optimizing away channels (ast_do_masquerade), that flag wasn't
copied.

In my case, using Local devices as queue members created a situation
where the endpoint was considered in use, but the state change of the
device being available again was ignored (not cached). The endpoint
channel was optimized into the (previously) Local channel, but kept
the do-not-cache flag. The end result being that the queue member
apparently stayed in use forever.

(closes issue ASTERISK-22718)
Review: https://reviewboard.asterisk.org/r/2925/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@401178 f38db490-d61c-443f-a65b-d21fe96a405b