samples: pktgen: Use "grep -E" instead of "egrep"

The latest version of grep claims the egrep is now obsolete so the build
now contains warnings that look like:
	egrep: warning: egrep is obsolescent; using grep -E
fix this up by moving the related file to use "grep -E" instead.

  sed -i "s/egrep/grep -E/g" `grep egrep -rwl samples/pktgen`

Here are the steps to install the latest grep:

  wget http://ftp.gnu.org/gnu/grep/grep-3.8.tar.gz
  tar xf grep-3.8.tar.gz
  cd grep-3.8 && ./configure && make
  sudo make install
  export PATH=/usr/local/bin:$PATH
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1668826504-32162-1-git-send-email-yangtiezhu@loongson.cnSigned-off-by: Paolo Abeni <pabeni@redhat.com>

samples/pktgen/functions.sh

@@ -191,7 +191,7 @@ function extend_addr6()
     fi
 
     # if shrink '::' occurs multiple, it's malformed.
-    shrink=( $(egrep -o "$sep{2,}" <<< $addr) )
+    shrink=( $(grep -E -o "$sep{2,}" <<< $addr) )
     if [[ ${#shrink[@]} -ne 0 ]]; then
         if [[ ${#shrink[@]} -gt 1 || ( ${shrink[0]} != $sep2 ) ]]; then
             err 5 "Invalid IP6 address: $1"