memif: fix the spinlock and unlock issue.
memif: fix the spinlock and unlock issue.

when the configuration of tx queues is larger than the worker-threads,
the clib_spinlock_lock_if_init will not be executed, and then this function
will executed the clib_spinlock_unlock_if_init, so this may caused the issue.

Type: fix

Signed-off-by: fangtong <8390953f60194f842bc295f6d2e6a27ea5ac70bf@163.com>
Change-Id: I3ce244cd5e1f410e9f14bd060b929238f069b9fa

FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp