network: selectively disable -Wcast-align in virNetDevParseDadStatus
    
    Commit 0f7436ca54c9 "network: wait for DAD to finish for bridge IPv6 addresses"
    results in:
    
     CC     util/libvirt_util_la-virnetdevmacvlan.lo
    util/virnetdev.c: In function 'virNetDevParseDadStatus':
    util/virnetdev.c:1319:188: error: cast increases required alignment of target type [-Werror=cast-align]
    util/virnetdev.c:1332:41: error: cast increases required alignment of target type [-Werror=cast-align]
    util/virnetdev.c:1334:92: error: cast increases required alignment of target type [-Werror=cast-align]
    cc1: all warnings being treated as errors
    
    on at least ARM platforms.
    
    The three macros involved (NLMSG_NEXT, IFA_RTA and RTA_NEXT) all appear to
    correctly take care of alignment, therefore suppress Wcast-align around their
    uses.
    
    Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    Cc: Maxim Perevedentsev <mperevedentsev@virtuozzo.com>
    Cc: Laine Stump <laine@laine.org>
    Cc: Dario Faggioli <dario.faggioli@citrix.com>
    Cc: Jim Fehlig <jfehlig@suse.com>