srp: leverage vlib_buffer_get_current
srp: leverage vlib_buffer_get_current

Change-Id: I8e4592734cd8343cd95b32ad8617fed4aec3f590
Signed-off-by: Zhiyong Yang <fbdb847fac8e5e50b588eb93d9ff9fd811b7568c@intel.com>

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