justify min()/max() macros declarations and usage

This change moves the macros to tcpdump-stdinc.h to make sure these are
available without interface.h. It also dismisses two redundant macros
MIN() and SMBMIN(). It is intended to fix the following Solaris compile
error:

Undefined                       first referenced
 symbol                             in file
MIN                                 print-zeromq.o