basic: Add our own <netinet/in.h> and <net/if.h> headers

basic: Add our own <netinet/in.h> and <net/if.h> headers

These glibc headers conflicts with the corresponding linux headers
(<linux/in.h> and <linux/if.h>) and impose an include order (the glibc one
has to be included before any linux header is included). This makes sorting
includes a royal pain so let's define our own versions of these headers using
various linux headers to do all the work and filling in the missing bits
ourselves.