Include for 'netinet/in.h' to NetUnix_p.h  allows compilatoin on FreeBSD

libbamtools won't compile on FreeBSD, throwing errors that `sockaddr_in`and others are not defined. It seems these variables are defined in `netinet/in.h` for FreeBSD. 

Adding this include means libbamtools compiles happily on both our FreeBSD machine and (still) on my Ubuntu box.