tests: Add bundle action test with buffer realloc.

tests: Add bundle action test with buffer realloc.

Add a test which causes internal reallocation of the ofpacts buffer,
followed by a large bundle action which should cause a subsequent
reallocation while decoding slave ports. Running this test under
valgrind reveals the issue below, which is fixed in the following
commit.

Invalid read of size 4
   at 0x4CED87: decode_bundle (ofp-actions.c:1253)
   by 0x4CEDFC: decode_NXAST_RAW_BUNDLE (ofp-actions.c:1272)
   by 0x4DBDE6: ofpact_decode (ofp-actions.inc2:3765)
   by 0x4D6914: ofpacts_decode (ofp-actions.c:5735)
   by 0x4D6A3D: ofpacts_pull_openflow_actions__ (ofp-actions.c:5772)
   by 0x4D74F3: ofpacts_pull_openflow_instructions (ofp-actions.c:6352)
   by 0x4F59FA: ofputil_decode_flow_mod (ofp-util.c:1704)
   by 0x4EAD18: ofp_print_flow_mod (ofp-print.c:786)
   by 0x4F0711: ofp_to_string__ (ofp-print.c:3220)
   by 0x4F0D98: ofp_to_string (ofp-print.c:3453)
   by 0x5486B3: do_recv (vconn.c:644)
   by 0x548498: vconn_recv (vconn.c:598)
   by 0x524582: rconn_recv (rconn.c:703)
   by 0x45DA61: ofconn_run (connmgr.c:1370)
   by 0x45B3B4: connmgr_run (connmgr.c:323)
   by 0x41D1E8: ofproto_run (ofproto.c:1762)
   by 0x40CEE0: bridge_run__ (bridge.c:2885)
   by 0x40D093: bridge_run (bridge.c:2940)
   by 0x412F7E: main (ovs-vswitchd.c:120)
Address 0x66aa460 is 1,152 bytes inside a block of size 1,184 free'd
   at 0x4C2AF2E: realloc (vg_replace_malloc.c:692)
   by 0x543D27: xrealloc (util.c:123)
   by 0x5089EF: ofpbuf_resize__ (ofpbuf.c:243)
   by 0x508B81: ofpbuf_prealloc_tailroom (ofpbuf.c:290)
   by 0x508D5C: ofpbuf_put_uninit (ofpbuf.c:364)
   by 0x508DEF: ofpbuf_put (ofpbuf.c:387)
   by 0x4CED7D: decode_bundle (ofp-actions.c:1255)
   by 0x4CEDFC: decode_NXAST_RAW_BUNDLE (ofp-actions.c:1272)
   by 0x4DBDE6: ofpact_decode (ofp-actions.inc2:3765)
   by 0x4D6914: ofpacts_decode (ofp-actions.c:5735)
   by 0x4D6A3D: ofpacts_pull_openflow_actions__ (ofp-actions.c:5772)
   by 0x4D74F3: ofpacts_pull_openflow_instructions (ofp-actions.c:6352)
   by 0x4F59FA: ofputil_decode_flow_mod (ofp-util.c:1704)
   by 0x4EAD18: ofp_print_flow_mod (ofp-print.c:786)
   by 0x4F0711: ofp_to_string__ (ofp-print.c:3220)
   by 0x4F0D98: ofp_to_string (ofp-print.c:3453)
   by 0x5486B3: do_recv (vconn.c:644)
   by 0x548498: vconn_recv (vconn.c:598)
   by 0x524582: rconn_recv (rconn.c:703)
   by 0x45DA61: ofconn_run (connmgr.c:1370)

Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Jarno Rajahalme <jarno@ovn.org>