bfdd: Prevent uninited use of data

bfdd: Prevent uninited use of data

Running valgrind w/ bfdd and shut/no shuting interfaces
can result in this valgrind issue:

==20279== Conditional jump or move depends on uninitialised value(s)
==20279==    at 0x115848: bfdd_sessions_enable_address (ptm_adapter.c:644)
==20279==    by 0x115848: bfdd_interface_address_update (ptm_adapter.c:674)
==20279==    by 0x48D8CAB: zclient_read (zclient.c:2698)
==20279==    by 0x48CCEE3: thread_call (thread.c:1603)
==20279==    by 0x48A84EF: frr_run (libfrr.c:1011)
==20279==    by 0x10DAC3: main (bfdd.c:236)
==20279==

When creating the bso data structure set the bso_isaddress to false
as a default value.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>