remove locking around tcpSesAllocCount atomic variable

The global tcpSesAllocCount variable is an atomic already and doesn't
really need the extra locking around it. Remove the locking and just use
the atomic_inc_return and atomic_dec_return functions to make sure we
access it correctly.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>