MINOR: session: rename sample fetch functions and declare the sample keywords

MINOR: session: rename sample fetch functions and declare the sample keywords

The following sample fetch functions were only usable by ACLs but are now
usable by sample fetches too :

  sc1_bytes_in_rate, sc1_bytes_out_rate, sc1_clr_gpc0, sc1_conn_cnt,
  sc1_conn_cur, sc1_conn_rate, sc1_get_gpc0, sc1_http_err_cnt,
  sc1_http_err_rate, sc1_http_req_cnt, sc1_http_req_rate, sc1_inc_gpc0,
  sc1_kbytes_in, sc1_kbytes_out, sc1_sess_cnt, sc1_sess_rate, sc1_trackers,
  sc2_bytes_in_rate, sc2_bytes_out_rate, sc2_clr_gpc0, sc2_conn_cnt,
  sc2_conn_cur, sc2_conn_rate, sc2_get_gpc0, sc2_http_err_cnt,
  sc2_http_err_rate, sc2_http_req_cnt, sc2_http_req_rate, sc2_inc_gpc0,
  sc2_kbytes_in, sc2_kbytes_out, sc2_sess_cnt, sc2_sess_rate, sc2_trackers,
  src_bytes_in_rate, src_bytes_out_rate, src_clr_gpc0, src_conn_cnt,
  src_conn_cur, src_conn_rate, src_get_gpc0, src_http_err_cnt,
  src_http_err_rate, src_http_req_cnt, src_http_req_rate, src_inc_gpc0,
  src_kbytes_in, src_kbytes_out, src_sess_cnt, src_sess_rate,
  src_updt_conn_cnt, table_avl, table_cnt,

The fetch functions have been renamed "smp_fetch_*".