zebra: fix use of freed es during zebra shutdown

zebra: fix use of freed es during zebra shutdown

This problem was reported by the sanitizer -
=================================================================
==24764==ERROR: AddressSanitizer: heap-use-after-free on address 0x60d0000115c8 at pc 0x55cb9cfad312 bp 0x7fffa0552140 sp 0x7fffa0552138
READ of size 8 at 0x60d0000115c8 thread T0
    #0 0x55cb9cfad311 in zebra_evpn_remote_es_flush zebra/zebra_evpn_mh.c:2041
    #1 0x55cb9cfad311 in zebra_evpn_es_cleanup zebra/zebra_evpn_mh.c:2234
    #2 0x55cb9cf6ae78 in zebra_vrf_disable zebra/zebra_vrf.c:205
    #3 0x7fc8d478f114 in vrf_delete lib/vrf.c:229
    #4 0x7fc8d478f99a in vrf_terminate lib/vrf.c:541
    #5 0x55cb9ceba0af in sigint zebra/main.c:176
    #6 0x55cb9ceba0af in sigint zebra/main.c:130
    #7 0x7fc8d4765d20 in quagga_sigevent_process lib/sigevent.c:103
    #8 0x7fc8d4787e8c in thread_fetch lib/thread.c:1396
    #9 0x7fc8d4708782 in frr_run lib/libfrr.c:1092
    #10 0x55cb9ce931d8 in main zebra/main.c:488
    #11 0x7fc8d43ee09a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2409a)
    #12 0x55cb9ce94c09 in _start (/usr/lib/frr/zebra+0x8ac09)
=================================================================

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>