wireshark: Use ${exec_prefix} instead of ${prefix}
wireshark: Use ${exec_prefix} instead of ${prefix}

${exec_prefix} and ${prefix} point to the same directory in
most setups, but when that's not the case the former should
be used for architecture-dependent data such as shared objects,
which makes it the best fit for our Wireshark dissector.

While at it, change all uses of $(var) to ${var}: they are
absolutely identicaly as far as make's concerned, but autoconf
itself seems to prefer the latter form so we might as well
follow suit.

andreabolognani/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,eskultety/libvirt,jardasgit/libvirt,libvirt/libvirt,olafhering/libvirt,datto/libvirt,nertpinx/libvirt,crobinso/libvirt,taget/libvirt,olafhering/libvirt,jardasgit/libvirt,nertpinx/libvirt,crobinso/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,libvirt/libvirt,VenkatDatta/libvirt,datto/libvirt,taget/libvirt,zippy2/libvirt,eskultety/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,crobinso/libvirt,eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,nertpinx/libvirt,datto/libvirt,jfehlig/libvirt,datto/libvirt,eskultety/libvirt,olafhering/libvirt,libvirt/libvirt,andreabolognani/libvirt,zippy2/libvirt,andreabolognani/libvirt,libvirt/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,taget/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,zippy2/libvirt,taget/libvirt,eskultety/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,zippy2/libvirt,jardasgit/libvirt,datto/libvirt,jfehlig/libvirt