net/lwip/ipv6: fix coding rule violation
net/lwip/ipv6: fix coding rule violation

This commit fixes violation of coding rule. The else conditional has no statement.
Let's remove it.

os/net/lwip/src/core/ipv6/nd6.c:2245: ERROR: [BRC_M_SMT] else should follow close brace '}'

Signed-off-by: sunghan-chang <c954e25285721d8faa8b1a5c1ae2ef5a35338d32@samsung.com>

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