fib: fix sa selection for fib routed destinations

fib: fix sa selection for fib routed destinations

The move from ip4(6)_src_address_for_packet to fib_sas4(6)_get changed
the behavior, so that the new looked only to adjacent gleans. This
caused a problem for destinations routed according to FIB table.

To reproduce:
vpp# create tap
vpp# set interface state tap0 up
vpp# set interface ip address tap0 192.168.11.1/24
vpp# ip route add 192.168.20.0/24 via 192.168.11.2

linux$ sudo ip addr add 192.168.20.1/24 dev lo
linux$ sudo ip link set tap0 up
linux$ sudo ip addr add 192.168.11.2/24 dev tap0

vpp# ping 192.168.20.1
Failed: no source address for egress interface

Type: fix
Signed-off-by: Július Milan <julius.milan@pantheon.tech>
Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: I22899f4dbbf8c1c85ccce72f801b92c183195b5d