Generalize get_ifb_associated_with_if's IFB name extraction regular expression

Instead of searching for a name like ifb0 by grepping for ifb followed by a digit,
extract the whole string starting with ifb up to (and excluding) the closing parenthesis
of "tc -p filter show parent ffff: dev $DEV" output. Example output follows:
filter protocol all pref 10 u32
filter protocol all pref 10 u32 fh 800: ht divisor 1
filter protocol all pref 10 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1
  match 00000000/00000000 at 0
	action order 1: mirred (Egress Redirect to device ifb1) stolen
 	index 19 ref 1 bind 1 installed 10 sec
 	Action statistics:
	Sent 2582 bytes 31 pkt (dropped 0, overlimits 0 requeues 0)
	backlog 0b 0p requeues 0
So do not use ) as part of the proper IFB name...