Add file_contexts entries for socket files.

So that we do not relabel them on a restorecon -R /data.

Change-Id: I6306a1e77922731a8f8d380345cefe6851bbc91c
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Move creation of /data/misc/wifi and /data/misc/dhcp to main init.rc file.

mkdir /data/misc/wifi subdirectories and /data/misc/dhcp is performed
in the various device-specific init*.rc files but seems generic.
Move it to the main init.rc file.

Change-Id: I51b09c5e40946673a38732ea9f601b2d047d3b62
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>