Fix HTC headset handling.

HTC's headset driver adds additional bits to the switch state, which
we're unable to deal with. Fix that by masking out those bits and
keeping only the valid ones.

Based off: https://gerrit.omnirom.org/#/c/5500/

Original author retained :)

Change-Id: I1abca665488e89f76eae97c4aab86bd51afd2a19
base: added national roaming for Aircel in India

Users of Aircel (Tamil Nadu) MCC 404-MNC 42 can roam on Aircel (Chennai)
MCC404-MNC41

Change-Id: Iaef2b8d634c13395c7328ba5a86b21ed9f39bfb9
base: added national roaming for telnet in belgium

http://jira.omnirom.org/browse/OMNI-682

Users of telnet (MCC 206 MNC 05) can roam in mobistar (MNC 10)

Change-Id: I8d2de1de0a9ba1ff792c3c28805aec078782c91e
base; added natiional roaming for Simyo in Spain

http://jira.omnirom.org/browse/OMNI-655

Users of Simyo (MCC 214 MNC 19) can roam on Orange (MNC03)

Change-Id: I39b0a3b933ad5a24c82ef33715bc0507c482574b
Merge changes I39b0a3b9,I8d2de1de,Iaef2b8d6,I1abca665 into du44

* changes:
  base; added natiional roaming for Simyo in Spain
  base: added national roaming for telnet in belgium
  base: added national roaming for Aircel in India
  Fix HTC headset handling.