net/avp: fix exported headers

net/avp: fix exported headers

This commit addresses several errors related to missing includes such as:

 In file included from /tmp/check-includes.sh.15315.c:1:0:
 build/include/rte_avp_fifo.h:77:22: error: 'struct rte_avp_fifo' declared
    inside parameter list [-Werror]
 [...]
 build/include/rte_avp_fifo.h: In function 'avp_fifo_init':
 build/include/rte_avp_fifo.h:81:3: error: implicit declaration of function
    'rte_panic' [-Werror=implicit-function-declaration]
 [...]
 build/include/rte_avp_fifo.h:83:6: error: dereferencing pointer to
    incomplete type
 [...]
 build/include/rte_avp_fifo.h:109:2: error: implicit declaration of
    function 'rte_wmb' [-Werror=implicit-function-declaration]
 [...]
 In file included from /tmp/check-includes.sh.15315.c:1:0:
 build/include/rte_avp_common.h:104:2: error: unknown type name 'uint64_t'
 [...]
 build/include/rte_avp_common.h:386:15: error: 'ETHER_ADDR_LEN' undeclared
    here (not in a function)
 [...]

It addresses errors with strict compilation flags:

 In file included from /tmp/check-includes.sh.15315.c:1:0:
 build/include/rte_avp_common.h:122:3: error: ISO C99 doesn't support
    unnamed structs/unions [-Werror=pedantic]
 [...]
 build/include/rte_avp_common.h:136:17: error: ISO C forbids zero-size
    array 'buffer' [-Werror=pedantic]
 [...]

And also adds C++ awareness to both header files.

Fixes: 8e680655e205 ("net/avp: add public header files")

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Allain Legacy <allain.legacy@windriver.com>