Changes

checkpatch.conf: lint more code

The current linter configuration leads to too many linting errors, as
seen here:
https://gerrit.osmocom.org/c/osmo-trx/+/42198/comments/f8f1b5a2_3c7e1389

Fix this by not excluding files where the linter generates false
positives. But instead ignoring specific rules that generate these false
positives (mostly related to this being a C++ code base). The following
rules are now ignored:

* SPACING
  Fails on:
    std::vector<std::string>
  With:
    ERROR:SPACING: spaces required around that '<' (ctx:VxV)
    ERROR:SPACING: spaces required around that '>' (ctx:VxW)

* FUNCTION_ARGUMENTS
  Fails on:
    ScopedLock lock(mLock);
  With:
    WARNING:FUNCTION_ARGUMENTS: function definition argument 'mLock' should also have an identifier name

* INDENTED_LABEL
  Fails on:
    private:
    protected:
  With:
    WARNING:INDENTED_LABEL: labels should not be indented

* NEW_TYPEDEFS
  Fails on:
    typedef std::map<K,D*> Map;
  With:
    WARNING:NEW_TYPEDEFS: do not add new typedefs

With the new config, the linter only complains about the following
things across the existing code, which seem to be legitimate linting
problems (and if not, can be ignored as well):

  BRACES_NOT_NECESSARY, CODE_INDENT, LEADING_SPACE,
  MULTISTATEMENT_MACRO_USE_DO_WHILE, OPEN_BRACE, POINTER_LOCATION,
  PRINTF_I_OSMO, SINGLE_STATEMENT_DO_WHILE_MACRO, SPACE_BEFORE_TAB,
  STATIC_CONST_CHAR_ARRAY, TABSTOP, TRAILING_WHITESPACE

Change-Id: I0df5b6f2f0bf1469a80a1f5859809c30f523f683