bgpd: aspath list format binds on as-notation format

bgpd: aspath list format binds on as-notation format

Each BGP prefix may have an as-path list attached. A forged
string is stored in the BGP attribute and shows the as-path
list output.

Before this commit, the as-path list output was expressed as
a list of AS values in plain format. Now, if a given BGP instance
uses a specific asnotation, then the output is changed:

new output:
router bgp 1.1 asnotation dot
!
 address-family ipv4 unicast
  network 10.200.0.0/24 route-map rmap
  network 10.201.0.0/24 route-map rmap
  redistribute connected route-map rmap
 exit-address-family
exit
!
route-map rmap permit 1
 set as-path prepend 1.1 5433.55 264564564
exit

ubuntu2004# do show bgp ipv4
BGP table version is 2, local router ID is 10.0.2.15, vrf id 0
Default local pref 100, local AS 1.1
Status codes:  s suppressed, d damped, h history, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

    Network          Next Hop            Metric LocPrf Weight Path
 *> 4.4.4.4/32       0.0.0.0                  0         32768 1.1 5433.55 4036.61268 ?
 *> 10.0.2.0/24      0.0.0.0                  0         32768 1.1 5433.55 4036.61268 ?
    10.200.0.0/24    0.0.0.0                  0         32768 1.1 5433.55 4036.61268 i
    10.201.0.0/24    0.0.0.0                  0         32768 1.1 5433.55 4036.61268 i

The changes include:
- the aspath structure has a new field: asnotation type
The ashash list will differentiate 2 aspaths using a different
asnotation.
- 3 new printf extensions display the as number in the wished
format: pASP, pASD, pASE for plain, dot, or dot+ format (extended).

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>