ioctl.c: FIX: must take io_sem around ecrt_master_send/ecrt_master_receive

Till Srequested to merge
paulscherrerinstitute/ethercat:fix_eoe_usermode_lock into stable-1.5

ecrt_master_send/ecrt_master_receive access data which are used from multiple threads (EOE, master). While all other calls from inside the master code lock 'io_sem' for protection/synchronization the 'ioctl' which is used by the user-mode library fails to do so. This patch adds the missing lock/unlock.

With this fix my application now runs for many hours while it would reproducibly crash within less than a minute.

Fixes issue #17 (closed)

Note that other branches (master,...) are also affected.

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