Changes

include/osmocom/netif/Makefile.am cosmetic: make it easier to extend

To make it easier to add new headers to osmonetif_HEADERS list,
make two cosmetic changes to it:

* List all currently exported headers in alphabetical order;
* Use $(NULL) construct so that every header-naming line ends
  with a backslash.

Change-Id: I05ecbdb44286b842e158278fb07479846cd66806

src/Makefile.am cosmetic: make it easier to extend

To make it easier to add new source files to libosmonetif_la_SOURCES
list, make two cosmetic changes to it:

* List stream.c before stream_{cli,srv}.c, matching the order
  that is used in other similar instances;
* Use $(NULL) construct so that every source-naming line ends
  with a backslash.

Change-Id: I98cf6d592fb66d5f22d486358ccdab06306ae3b0