$" is a BASH extension to translate text.
Replace the shebang with /bin/bash to avoid parsing errors,
as even BASH has a POSIX compliant mode when run as sh.

Signed-off-by: Matteo Croce <mcroce@redhat.com>

network-functions uses awk to tranform the mac address to upper case.
Replace awk with tr which is two order of magnitude faster:

    $ time awk '{ print toupper($0) }' </usr/share/dict/words >/dev/null

    real    0m0,227s
    user    0m0,224s
    sys     0m0,004s
    $ time tr '[a-z]' '[A-Z]' </usr/share/dict/words >/dev/null

    real    0m0,005s
    user    0m0,000s
    sys     0m0,005s

Also use here-strings instead of spawning a subshell and a pipe.

Signed-off-by: Matteo Croce <mcroce@redhat.com>

  Instead of displaying messages without context, like this:

  ./network-functions: line 571: echo: write error: Invalid argument
  ./network-functions: line 598: echo: write error: Permission denied

  We will now display pretty error messages (via net_log) about what has
  actually failed...

  Previously, there were 2 additional conditions related to this part of
  code, but they were removed in time, so this last condition has
  remained an artifact and is de-facto obsolete.

  However, the 'pidof -x dhclient' condition could cause the network
  service to hang on stop/restart when processes were executed from a
  network share... Removing that condition should hypothetically fix it.

* ifup-tunnel: Support 'external' tunnels

This is a newish feature upstream. You can now set the external flag on a
ip6_tunnel type interface (though not the primary one, ip6tnl0), and doing so
will allow it to decapsulate any packet, and assuming that the inner address is
the one on that interface, it'll drop it back on the stack.

This is useful for DSR vips. While v6-in-v6 was already supported, this allows
v4-in-v6 which is necessary to serve v4 traffic in a v6only infrastructure.

There's comments in ifup-tunnel that imply it was designed only for GRE tunnels,
but this still seems like the best place for this.

  Empty ${RESOLV_MODS} was causing a deletion of config files in
  /etc/ppp/peers/*

  Resolves: #155

  This is complete rework of how we generate the /etc/resolv.conf.

  Fixes:
   * always update 'nameserver' & 'search' entries when DNS* & DOMAIN
     options (respectively) were updated in ifcfg-* files
   * always update the order of 'nameserver' entries when the order of
     DNS* options was updated
   * always keep /etc/resolv.conf.save as a proper backup - do not
     overwrite it everytime when updating 'nameserver' or 'search'

  Enhancements:
   * added support for DNS3 option (equals to MAXNS value in GLIBC)
   * added logic to process duplicate DNS* options
   * added logic to process randomly omitted DNS* options (e.g. omitting
     DNS1 while specifying DNS2 and/or DNS3 will still work now)

  This work was based on these two RHEL-7.5 BZs:
  https://bugzilla.redhat.com/show_bug.cgi?id=1364895
  https://bugzilla.redhat.com/show_bug.cgi?id=1357658