Update git submodules

* Update src/sonic-quagga from branch 'broadcom_sonic'
  to 46a93c34f452b87434913e624f1f9d1052379595
  - Merge 201904 branch to broadcom_sonic branch on Mon Jul  1 13:57:55 PDT 2019
    
    Change-Id: I74f1c79dedbf8edbf3fbacfd2f52df8d75c644a5
    
  - Don't create duplicate dynamic BGP sessions. (#36)
    
    Sometimes dynamic BGP peers setup another TCP connection despite they already have one.
    
    When quagga receives second tcp connection from the same dynamic peer, quagga pick up struct peer structure for the dynamic peer, instead of creating of the new one (because it's dynamic peer, not static).
    
    So quagga has two tcp connections, but they share the same peer structure.
    Later quagga realize that it already has bgp session is created for the peer, and quagga removes the peer structure, but the first connection is still active. The first connection tries to use the removed peer structure and bgpd crashes.