classify: Fix 2 coverity errors
classify: Fix 2 coverity errors

Validate two tainted scalars, filter_sw_if_index, that
came from an API message.

Type: fix
Change-Id: I3ac8a09f91f380185e36babeaa6330691f7cb24b
Signed-off-by: Jon Loeliger <2c20cf3f4bac0d9467d3fe2c932e4d1e1bc1f44c@netgate.com>

vpp-dev/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp