[Platform][AS7326-56X][AS7726-32X]: Fix pytest of port toggle test item failed.

Why I did it:
    Testbed pytest port toggle failed on topology t0.
    When deploy t0's minigraph by 'config load_minigraph -y',
    the syncd occurs error so that most docker containers(synd, swss, ...) are not running.
    And the syslog exists the below entry:
    - ERR syncd#syncd: [none] SAI_API_NEXT_HOP_GROUP:brcm_sai_xgs_nexthop_group_create:113 ecmp nh group create failed with error Feature unavailable (0xfffffff0)

How I dit it:
    Setup broadcom soc property l3_ecmp_levels=2 refer to as4630-54pe, as4630-54te, and as5835-54x.

How to verify it:
    Re-run pytest port toggle is pass and no syncd sai feature unavailable log exists in syslog.

Author: tiger_fu

device/accton/x86_64-accton_as7326_56x-r0/Accton-AS7326-56X/td3-as7326-48x25G+8x100G.config.bcm

@@ -33,6 +33,7 @@ tdma_timeout_usec=3000000
 skip_L2_USER_ENTRY=0
 bcm_tunnel_term_compatible_mode=1
 l3_alpm_ipv6_128b_bkt_rsvd=1
+l3_ecmp_levels=2
 
 #vxlan
 use_all_splithorizon_groups=1

device/accton/x86_64-accton_as7726_32x-r0/Accton-AS7726-32X/td3-as7726-32x100G.config.bcm

@@ -35,6 +35,7 @@ skip_L2_USER_ENTRY=0
 bcm_tunnel_term_compatible_mode=1
 l3_alpm_ipv6_128b_bkt_rsvd=1
 phy_an_c73=1
+l3_ecmp_levels=2
 
 use_all_splithorizon_groups=1
 riot_enable=1