osd: fix recursive map_lock via check_replay_queue()

osd: fix recursive map_lock via check_replay_queue()

Also drop activate_pg() helper while we're at it, so it's clear that we
are the only user.

recursive lock of OSD::map_lock (33)
 ceph version 0.42-146-g7ad35ce (commit:7ad35ce489cc5f9169eb838e1196fa2ca4d6e985)
2012-02-24 12:30:16.541416 1: (PG::lock(bool)+0x2a) [0xa09348]
2012-02-24 12:30:16.541424 2: (OSD::_lookup_lock_pg(pg_t)+0xbd) [0x84b8df]
2012-02-24 12:30:16.541431 3: (OSD::activate_pg(pg_t, utime_t)+0x9f) [0x87463b]
2012-02-24 12:30:16.541442 4: (OSD::check_replay_queue()+0x12f) [0x87452d]
2012-02-24 12:30:16.541450 5: (OSD::tick()+0x23c) [0x8535ea]
2012-02-24 12:30:16.541456 6: (OSD::C_Tick::finish(int)+0x1f) [0x881671]
2012-02-24 12:30:16.541462 7: (SafeTimer::timer_thread()+0x2d5) [0x8f8211]
2012-02-24 12:30:16.541468 8: (SafeTimerThread::entry()+0x1c) [0x8f923c]
2012-02-24 12:30:16.541475 9: (Thread::_entry_func(void*)+0x23) [0x9c8109]
2012-02-24 12:30:16.541485 10: (()+0x68ba) [0x7f9dbed838ba]
2012-02-24 12:30:16.541491 11: (clone()+0x6d) [0x7f9dbd66f02d]
2012-02-24 12:30:16.541495 common/lockdep.cc: In function 'int lockdep_will_lock(const char*, int)' thread 7f9db9d98700 time 2012-02-24 12:30:16.541504

Signed-off-by: Sage Weil <sage.weil@dreamhost.com>
Reviewed-by: Sam Just <samuel.just@dreamhost.com>