Make sure that the netlink socket will never block after program

initialization.  Fetching if/address/index/mac mappings is done only once at
program init, so it is done synchronously as an exception to this rule.

Rewrite the netlink handling.  Now uses NIH code that should be safe, small,
and correct.  No external deps FTW.

CMakeLists.txt

@@ -7,8 +7,6 @@ set(CMAKE_CXX_FLAGS "${CMAKE_C_FLAGS} -s -std=gnu99 -pedantic -Wall -lcap -DHAVE
 
 include_directories("${PROJECT_SOURCE_DIR}/ncmlib")
 add_subdirectory(ncmlib)
-include_directories("${PROJECT_SOURCE_DIR}/libmnl")
-add_subdirectory(libmnl)
 
 add_subdirectory(ifchd)
 add_subdirectory(ndhc)