selftests: net: Remove unnecessary backslashes in fq_band_pktlimit.sh

selftests: net: Remove unnecessary backslashes in fq_band_pktlimit.sh

Address "grep: warning: stray \ before white space" warning from GNU
grep 3.12. This warns the misplaced backslashes before whitespaces
(e.g. \\' ' or '\ ') which leads to unspecified behavior [1].

We can just remove the backslashes before whitespaces as POSIX says:

  Enclosing characters in single-quotes ('') shall preserve the literal
  value of each character within the single-quotes.

and bourne-compatible shells behave so.

[1]: https://lists.gnu.org/r/bug-gnulib/2022-05/msg00057.html

Signed-off-by: Yohei Kojima <yk@y-koj.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/dd0bbd48cdf468da56ec34fd61cecd4d2111d7ba.1774372510.git.yk@y-koj.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>