Pullup ticket #6410 - requested by kardel
net/frr: build fix

Revisions pulled up:
- net/frr/Makefile                                              1.3-1.4

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  Module Name:    pkgsrc
  Committed By:  kardel
  Date:          Wed Jan  6 10:45:49 UTC 2021

  Modified Files:
          pkgsrc/net/frr: Makefile

  Log Message:
  net/frr: document bison tool dependency

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  Module Name:    pkgsrc
  Committed By:  kardel
  Date:          Wed Jan  6 11:53:52 UTC 2021

  Modified Files:
          pkgsrc/net/frr: Makefile

  Log Message:
  net/frr: simplify bison tool requirement

(bsiegert)