Drop packet if there are not enough free buffers to perform fragmentation
Improve csma debug traces
Add per neighbor packet throttle
Add function to change I2C baudrate and push relevant configuration values to platform config
Merge pull request #825 from alignan/i2c_changes

Add function to change I2C baudrate and push relevant configuration valu...
Merge pull request #648 from cetic/pr-csma-fixes

High throughput fixes for csma and sixlowpan
Makefile.include: Assign git description variable once.

By changing RELSTR= into RELSTR:= we force Make to evaluate the Git
version string only during Makefile read, and not on every single build
command execution.

The reduction in file system I/O cut the time to build
examples/er-rest-example on my development machine by a significant
amount, see below.

Core i7 notebook with ext4 file system on an SSD (building for TARGET=mulle):
"RELSTR="  make  19.70s user 1.07s system 82% cpu 25.291 total
"RELSTR:=" make  11.81s user 1.27s system 79% cpu 16.499 total

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
Merge pull request #841 from gebart/build-git-tag-io-reduce

Makefile.include: Reduce I/O load (and build time) by assigning git description variable once.