Ensure that packet is set to p param to type of bytes. In certain sit…

[muttiopenbts]

Checklist:

• [x] If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• [x] I squashed commits belonging together
• [x] I executed the regression tests (using cd test && ./run_tests or tox)

Ensure that params that representing packets are set to type bytes. In certain situations where bgp fields for open messages were being set, this function was initializing packet variable to a str and returning.

Fix bgp path_attrib length field. Should be type byte, not int.

Adding fuzz() support to bgp open and update.

Allow for BGPFieldLenField len to be fuzzed, but fixed when recalled.