vpp: fix race condition causing syncd crash

[yue-fred-gao]

Description of PR

Summary:
Fixes a race condition during init_switch causing syncd crash

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation update
• Test improvement

Approach

What is the motivation for this PR?

We saw below core dump during init_switch.

#0  0x0000ffffb5c369d0 in vpp_ev_enqueue (ev=0xaaaabe182c50) at vpp/vppxlate/SaiVppXlate.c:397
#1  vl_api_sw_interface_event_t_handler (mp=<optimized out>) at vpp/vppxlate/SaiVppXlate.c:687
#2  0x0000ffffb5264470 in vl_msg_api_handler_no_free ()
   from /nobackup/yuega2/sonic-buildimage-cisco.202603.arctos-periodic-40135/syncd_dbg/rootfs/lib/aarch64-linux-gnu/libvlibapi.so.25.02.0
#3  0x0000ffffb5205648 in ?? ()
   from /nobackup/yuega2/sonic-buildimage-cisco.202603.arctos-periodic-40135/syncd_dbg/rootfs/lib/aarch64-linux-gnu/libvlibmemoryclient.so.25.02.0
#4  0x0000ffffb5c3cd54 in vpp_intf_events_enable_disable (enable=true) at vpp/vppxlate/SaiVppXlate.c:1839
#5  init_vpp_client () at vpp/vppxlate/SaiVppXlate.c:1704
#6  0x0000ffffb5c208bc in saivs::SwitchVpp::vpp_dp_initialize (this=this@entry=0xaaaabe17a3d0) at vpp/SwitchVppRif.cpp:468
#7  0x0000ffffb5c0508c in saivs::SwitchVpp::SwitchVpp (this=this@entry=0xaaaabe17a3d0, switch_id=switch_id@entry=141733920768, manager=..., config=..., 
    warmBootState=...) at vpp/SwitchVpp.cpp:44

This happened during init_switch right after vpp_intf_events_enable_disable, an event came in but event_queue had not been properly initialized.

Work item tracking

• Microsoft ADO (number only):

How did you do it?

Move event queue initialization before enabling events from vpp.

How did you verify/test it?

Run sonic-mgmt via sonic-net/sonic-buildimage#27039

Any platform specific information?

vpp specific

Documentation

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

Cherry-pick PR to msft-202603: Azure/sonic-sairedis.msft#127