core: rmnet: Fastforward to 4.19 tip

This brings the RmNet and DFC modules up to date with the 4.19 tip as of
commit 9b38611ea527 ("rmnet: Reduce synchronize_rcu calls").

As part of this, the rmnet_ctl driver was also incorporated, using commit
4ceee3aafb7d ("rmnet_ctl: Add IPC logging and optimizations")

Change-Id: Ic45d46074c7401dfed408c769cfb6462dac0d4ee
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>