eigrp: use correct memory pool on interface deletion

eigrp: use correct memory pool on interface deletion

Trying to delete an interface during the test test_eigrp_topo1.py triggers a crash.
```
EIGRP: abort+0x12b
EIGRP: _zlog_assert_failed+0x18c
EIGRP: mt_count_free+0x56
EIGRP: qfree+0x2e
EIGRP: eigrp_if_delete_hook+0x8c
EIGRP: hook_call_if_del+0x5f
EIGRP: if_delete_retain+0x1c
EIGRP: if_delete+0xfb
EIGRP: if_destroy_via_zapi+0x69
EIGRP: zclient_interface_delete+0x57
EIGRP: zclient_read+0x3d0
EIGRP: event_call+0xd8
EIGRP: frr_run+0x271
EIGRP: main+0x14b
EIGRP: __libc_start_main+0xf3
EIGRP: _start+0x2e
EIGRP: in thread zclient_read scheduled from lib/zclient.c:4514 zclient_event()
```

Signed-off-by: Volodymyr Huti <v.huti@vyos.io>