maint: use consistent if-else braces in conf and friends
    
    I'm about to add a syntax check that enforces our documented
    HACKING style of always using matching {} on if-else statements.
    
    This patch focuses on code shared between multiple drivers.
    
    * src/conf/domain_conf.c (virDomainFSDefParseXML)
    (virSysinfoParseXML, virDomainNetDefParseXML)
    (virDomainWatchdogDefParseXML)
    (virDomainRedirFilterUSBDevDefParseXML): Correct use of {}.
    * src/conf/interface_conf.c (virInterfaceDefParseDhcp)
    (virInterfaceDefParseIp, virInterfaceVlanDefFormat)
    (virInterfaceDefParseStartMode, virInterfaceDefParseBondMode)
    (virInterfaceDefParseBondMiiCarrier)
    (virInterfaceDefParseBondArpValid): Likewise.
    * src/conf/node_device_conf.c (virNodeDevCapStorageParseXML):
    Likewise.
    * src/conf/nwfilter_conf.c (virNWFilterRuleDetailsParse)
    (virNWFilterRuleParse, virNWFilterDefParseXML): Likewise.
    * src/conf/secret_conf.c (secretXMLParseNode): Likewise.
    * src/cpu/cpu_x86.c (x86Baseline, x86FeatureLoad, x86ModelLoad):
    Likewise.
    * src/network/bridge_driver.c (networkKillDaemon)
    (networkDnsmasqConfContents): Likewise.
    * src/node_device/node_device_hal.c (dev_refresh): Likewise.
    * src/nwfilter/nwfilter_gentech_driver.c (virNWFilterInstantiate):
    Likewise.
    * src/nwfilter/nwfilter_ebiptables_driver.c
    (_iptablesCreateRuleInstance): Likewise.
    * src/storage/storage_backend_disk.c
    (virStorageBackendDiskBuildPool): Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>