telephony: SignalStrengh: Don't calculate a LTE snr if the srq is invalid

If the previous values are invalid and signal quality is -1, chances are there's
no LTE signal at all, so don't calculate the SNR and mark it invalid as well.

This fixes the strength indicator in GSM devices where it was being skewed
by the ghost LTE value

Change-Id: I070573401c141aa99941a332ee256246697abb90
base: added national roaming info for Play in Poland

Cherry-picked from OmniROM:
https://gerrit.omnirom.org/#/c/3382/

Users of Play in Poland (MCC 260 MNC 06) can roam on
Plus, T-Mobile, Orange (MNCs 01/02/03)

Change-Id: I8ea62b0ca40bac9ced11802ee8ef583d6392a199
National roaming info for Drei in Austria

3AT roams in T-Mobile AT networks

Change-Id: I915edccf92bcbb088fa25b958eb345c624f61597
National roaming info for yesss! in Austria

Change-Id: I930198d3cb311b23752a8c2f54852ebd48d65b86
National roaming info for 3 in Ireland

Change-Id: I451831f4144b72feac1a38ef1e8693cb947d6d7e
core: added national roaming info for Tesco Mobile in Ireland.

Users of Tesco Mobile in Ireland(MCC 272 MNC 11)
  can roam on O2 Ireland (MNC 02)

Change-Id: Ie0b32d51511c2bbc726c43cdec78332397d1ecb9
core: added national roaming info for Bob in Austria.

Users of Bob in Austria(MCC 232 MNC 11)
  can roam on A1 Austria (MNC 01)

Change-Id: I12dfa3d63643af1026dcfea28a4c9d7acec5f9e9
core: added national roaming info for Spring Mobil in Sweden...

Spring Mobil users in Sweden (MCC 240, MNC 10)
can roam on Sweden 3G (MNC 05) and on Sweden 2G (MNC 24).

Change-Id: Ie27ad3561de32557a1713d4962fcc9ec52a8b7fe
National roaming for Telfort in the Netherlands

Don't roam on KPN.nl (204/08)

Change-Id: I4b7614bcdf679bbcb8822077c32d97117d878a8a
Added Non-Roaming for carrier BSNL in UP East and WEST INDIA

Added No-roaming for BSNL from circle UP East to UP West, India

Change-Id: I45e804da143e844d794cca98652f5fc6ac4e209b
Allow 3 AT (mnc05) to roam on T-Mobile in Austria

Change-Id: Ie1a62db9a48cfaf594ddda7b413299a9b587ddd4
National Roaming: Allow T-Mobile AT (MNC03) to roam on 3 AT (MNC10) in Austria

Change-Id: Ief827259fdcb5bfa13bd643f80a8547a56cc934c
Saunalahti considered non-roaming on Elisa

Change-Id: I51b554cf578c6027d52ad6e111e41d269c1f579f
Tele2 considered non-roaming on T-Mo

Change-Id: Ibb05f277b701861b8716168b54e96f63127e686d
Noverca (MNC07) considered non-romaing on TIM (MNC01)

Change-Id: I473e1f88db0fe0d5e1799f6d6d892649abb7dc74
Virgin Mobile (MNC07) considered non-roaming on Movistar (MNC02)

Change-Id: I46a782aefbe62295d6ce9d3c15a2e25630bdcacc
Vectone/Delight (MNC07) considered non-roaming on NOS (MNC03)

Change-Id: I743935b94bb531d78b784550e3028378cdc01959
Lycamobile (MNC04) considered non-roaming on Vodafone (MNC01)

Change-Id: Icff916672e5ed666adf2cdfeb26d24bf43b64683
add MVNO info for tele2 in croatia
per CYAN-5178

Change-Id: I80f8bfbcf0f40abac397ddf63beaf2c0b2e46dfd
Vectone UK (MNC01) considered non-roaming on T-Mobile (MNC30)

Change-Id: Id74c854f958be721be12451a124cfd2f8b150255