net: ip_rt_get_source() - use new style struct initializer instead of memset

[ Upstream commit e351bb6227fbe2bb5da6f38a4cf5bd18810b0557 ]

(allows for better compiler optimization)

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: cc73bbab4b1f ("ipv4: Fix incorrect source address in Record Route option")
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 0e8712254b48a7c6ebb76dce414a9539e772d406)
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>