Update APNs for au, docomo, SoftBank and Y!mobile (Japan)

Change-Id: I9d9636cfb14526128f746d8c623c5714c1a1037c
Add APNs for docomo MVNOs (Japan)

@nifty: http://support.nifty.com/support/manual/internet/dolte/
BB.excite: http://support.excite.co.jp/app/answers/detail/a_id/3090
BIGLOBE: http://support.biglobe.ne.jp/settei/setuzoku/lte/index.html
DTI: http://dream.jp/mb/sim/support/manual/mnl_and_01.html
OCN: http://tech.support.ntt.com/ocn/mobile/one/
So-net: http://faq.so-net.ne.jp/app/answers/detail/a_id/2920/
U-mobile: http://umobile.jp/service/sim/setting/
WirelessGate: http://www.wirelessgate.co.jp/sim/service/yd/start_apn
hi-ho: http://home.hi-ho.ne.jp/hihomobile/lte/d/index.html?page=setting
楽天 エントリー/ライト/アクティブ: http://broadband.rakuten.co.jp/support/manual_internet/lte/android.html

Change-Id: I42d84cb7396029b974e63d8c39c94ade20247893
added Walmart APN

Change-Id: Ic9392cefde2cf6e6c3a00d77d3e4a91d2de7a7c1